全文获取类型
收费全文 | 1479篇 |
免费 | 96篇 |
国内免费 | 2篇 |
出版年
2023年 | 7篇 |
2022年 | 29篇 |
2021年 | 42篇 |
2020年 | 16篇 |
2019年 | 24篇 |
2018年 | 47篇 |
2017年 | 31篇 |
2016年 | 53篇 |
2015年 | 72篇 |
2014年 | 81篇 |
2013年 | 108篇 |
2012年 | 106篇 |
2011年 | 93篇 |
2010年 | 68篇 |
2009年 | 50篇 |
2008年 | 68篇 |
2007年 | 68篇 |
2006年 | 83篇 |
2005年 | 59篇 |
2004年 | 51篇 |
2003年 | 41篇 |
2002年 | 28篇 |
2001年 | 28篇 |
2000年 | 26篇 |
1999年 | 20篇 |
1998年 | 13篇 |
1997年 | 6篇 |
1996年 | 15篇 |
1995年 | 7篇 |
1994年 | 8篇 |
1993年 | 10篇 |
1992年 | 27篇 |
1991年 | 22篇 |
1990年 | 20篇 |
1989年 | 17篇 |
1988年 | 19篇 |
1987年 | 16篇 |
1986年 | 13篇 |
1985年 | 11篇 |
1984年 | 7篇 |
1983年 | 4篇 |
1981年 | 4篇 |
1979年 | 10篇 |
1978年 | 3篇 |
1976年 | 6篇 |
1974年 | 5篇 |
1973年 | 4篇 |
1971年 | 4篇 |
1970年 | 6篇 |
1969年 | 5篇 |
排序方式: 共有1577条查询结果,搜索用时 343 毫秒
141.
Presence of adrenocorticotropic hormone (ACTH) was investigated in tissues from 150 cases of primary breast cancer. ACTH peptides were detected in 16.7% cases and ACTH expression was higher in post-menopausal cancers. A significant association was noticed between the presence of ACTH and the positive estrogen receptor (ER) status of tumors. The study indicated a probable role of these ectopic ACTH peptides in steroid hormone related pathology of breast cancer. 相似文献
142.
Chattopadhyay D Dungdung SR Das K Saha S Mandal AB Majumder GC 《Indian journal of experimental biology》2005,43(11):1104-1109
The role of methanolic extract and n-butanol fraction of A. macrophylla leaves was investigated on the forward motility of goat spermatozoa. The methanol extract (600 micro/g/ml) and one n-butanol fraction (Fraction A; 100 microg/ml) showed marked inhibition of sperm forward motility, tested by microscopic and spectrophotometric methods. Approximately, 50-60% of the spermatozoa lost their motility when treated with 600 microg/ml of methanol extract or 100 microg/ml of Fraction A. The Fraction A at 400 microg/ml concentration showed complete inhibition of sperm forward motility at 0 min. The inhibitory activity increased with the increasing concentrations of the fraction. The motility inhibitory activity of the Fraction A was stable to heat treatment at 100 degrees C for 2 min. The compound showed high inhibitory effect in the pH range 6.7-7.6. Fraction A also showed high efficacy for inhibiting human sperm motility, assessed by the microscopic method. The phytochemical analysis of methanolic extract of A. macrophylla leaves revealed the presence of sterols, triterpene, flavonoid, alkaloid, tannin and reducing sugar, while the Fraction A contains beta-sitosterol, a common phytosterol. The results demonstrate that Fraction A (beta-sitosterol) is a potent inhibitor of sperm motility and thus it has the potential to serve as a vaginal contraceptive. 相似文献
143.
Miguel Quintana Peter Lindell Samir K Saha Francesca del Furia Britta Lind Satish Govind Lars-Åke Brodin 《Cardiovascular ultrasound》2005,3(1):1-12
Background
Myocardial contrast echocardiography and coronary flow velocity pattern with a rapid diastolic deceleration time after percutaneous coronary intervention has been reported to be useful in assessing microvascular damage in patients with acute myocardial infarction.Aim
To evaluate myocardial contrast echocardiography with harmonic power Doppler imaging, coronary flow velocity reserve and coronary artery flow pattern in predicting functional recovery by using transthoracic echocardiography.Methods
Thirty patients with anterior acute myocardial infarction underwent myocardial contrast echocardiography at rest and during hyperemia and were quantitatively analyzed by the peak color pixel intensity ratio of the risk area to the control area (PIR). Coronary flow pattern was measured using transthoracic echocardiography in the distal portion of left anterior descending artery within 24 hours after recanalization and we assessed deceleration time of diastolic flow velocity. Coronary flow velocity reserve was calculated two weeks after acute myocardial infarction. Left ventricular end-diastolic volumes and ejection fraction by angiography were computed.Results
Pts were divided into 2 groups according to the deceleration time of coronary artery flow pattern (Group A; 20 pts with deceleration time ≧ 600 msec, Group B; 10 pts with deceleration time < 600 msec). In acute phase, there were no significant differences in left ventricular end-diastolic volume and ejection fraction (Left ventricular end-diastolic volume 112 ± 33 vs. 146 ± 38 ml, ejection fraction 50 ± 7 vs. 45 ± 9 %; group A vs. B). However, left ventricular end-diastolic volume in Group B was significantly larger than that in Group A (192 ± 39 vs. 114 ± 30 ml, p < 0.01), and ejection fraction in Group B was significantly lower than that in Group A (39 ± 9 vs. 52 ± 7%, p < 0.01) at 6 months. PIR and coronary flow velocity reserve of Group A were higher than Group B (PIR, at rest: 0.668 ± 0.178 vs. 0.248 ± 0.015, p < 0.0001: during hyperemia 0.725 ± 0.194 vs. 0.295 ± 0.107, p < 0.0001; coronary flow velocity reserve, 2.60 ± 0.80 vs. 1.31 ± 0.29, p = 0.0002, respectively).Conclusion
The preserved microvasculature detecting by myocardial contrast echocardiography and coronary flow velocity reserve is related to functional recovery after acute myocardial infarction. 相似文献144.
The kinetics of Cr(VI) oxidation of D-glucose to the corresponding lactone in the presence and absence of 2,2'-bipyridine (bipy) has been carried out under the conditions, [D-glucose](T) > [Cr(VI)](T) at different temperatures in aqueous micellar media. The monomeric Cr(VI) species has been found to be kinetically active in the absence of bipy whereas in the bipy-catalysed path, the Cr(VI)-bipy complex has been found to be the active oxidant. In the bipy-catalysed path, the Cr(VI)-bipy complex undergoes nucleophilic attack by the substrate to form a ternary complex. The ternary complex spontaneously experiences a redox decomposition (through two-electron transfer) in the rate-determining step leading to the product lactone and Cr(IV)-bipy complex. The Cr(IV)-bipy complex then takes part in faster steps in the further oxidation of D-glucose and is ultimately converted into a Cr(III)-bipy complex. In the uncatalysed path, the Cr(VI)-substrate ester experiences acid catalysed redox decomposition (two-electron transfer) in the rate-determining step. The uncatalysed path shows a second order dependence on [H(+)] and a first order dependence on each of the reactants [D-glucose](T) and [Cr(VI)](T). In contrast, the bipy-catalysed path shows a first order dependence on each of the reactants [H(+)], [D-glucose](T) and [Cr(VI)](T). The bipy-catalysed path is first order in [bipy](T). These observations remain unaltered in the presence of externally added surfactants. The effect of the cationic surfactant, N-cetylpyridinium chloride (CPC) and anionic surfactant, sodium dodecyl sulfate (SDS) on both the uncatalysed and bipy-catalysed path has been studied. CPC inhibits both the uncatalysed and bipy-catalysed path, while SDS catalyses these reactions. The observed micellar effects have been explained by considering hydrophobic and electrostatic interactions between the surfactants and reactants. 相似文献
145.
Abdurakhmonov IY Abdullaev AA Saha S Buriev ZT Arslanov D Kuryazov Z Mavlonov GT Rizaeva SM Reddy UK Jenkins JN Abdullaev A Abdukarimov A 《The Journal of heredity》2005,96(6):644-653
Cotton (Gossypium hirsutum L.) leaf defoliation has a significant ecological and economical impact on cotton production. Thus the utilization of a natural leaf defoliation trait, which exists in wild diploid cotton species, in the development of tetraploid cultivated cotton will not only be cost effective, but will also facilitate production of very high-grade fiber. The primary goal of our research was to tag loci associated with natural leaf defoliation using microsatellite markers in Upland cotton. The F2 populations developed from reciprocal crosses between the two parental cotton lines--AN-Boyovut-2 (2n = 52), a late leaf defoliating type, and Listopad Beliy (2n = 52), a naturally early leaf defoliating type--demonstrated that the naturally early leaf defoliation trait has heritability values of 0.74 and 0.84 in the reciprocal F2 population. The observed phenotypic segregation difference in reciprocal crosses suggested a minor cytoplasmic effect in the phenotypic expression of the naturally early leaf defoliation trait. Results from the Kruskal-Wallis (KW) nonparametric test revealed that JESPR-13 (KW = 6.17), JESPR-153 (KW = 9.97), and JESPR-178 (KW = 13.45) Simple sequence repeat (SSR) markers are significantly associated with natural leaf defoliation in the mapping population having stable estimates at empirically obtained critical thresholds (P < .05-.0001). JESPR-178 revealed the highest estimates (P < .0001) for association with the natural leaf defoliation trait, exceeding maximum empirical threshold values. JESPR-178 was assigned to the short arm of chromosome 18, suggesting indirectly that genes associated with natural leaf defoliation might be located on this chromosome. This microsatellite marker may have the potential for use to introgress the naturally early leaf defoliation quantitative trait loci (QTL) from the donor line Listopad Beliy to commercial varieties of cotton through marker-assisted selection programs. 相似文献
146.
Suchankova G Tekle M Saha AK Ruderman NB Clarke SD Gettys TW 《Biochemical and biophysical research communications》2005,326(4):851-858
Polyunsaturated fatty acids (PUFA) and a number of drugs (metformin, thiazolidinediones) and hormones (leptin, adiponectin) that activate AMP-activated protein kinase (AMPK) have been reported to improve insulin sensitivity. To determine whether PUFA activate AMPK, Sprague-Dawley rats were adapted to a 3h meal-feeding regimen using a fat-free diet (FFD) supplemented with fish oil (n-3) or triolein (n-9) for 7 days. No differences in hepatic AMPK activity were observed between the groups after 21h of fasting. On the other hand, hepatic AMPK phosphorylation was decreased in rats refed the FFD, the FFD+triolein, and the FFD+PUFA by 80%, 75%, and 50%, respectively, when assessed 2h after completion of a meal. In keeping with these changes, decreases in acetyl-CoA carboxylase phosphorylation and carnitine palmitoyl transferase-1 mRNA and increases in fatty acid synthase gene expression were greatest in rats fed the FFD and least in the PUFA-fed rats. The results indicate that dietary PUFA enhance hepatic AMPK activity in vivo, and implicate AMPK as a component of the nutrient-sensing mechanism through which dietary fatty acids and especially PUFA influence the regulation of hepatic lipid metabolism and gene expression. 相似文献
147.
O'Connell RM Vaidya SA Perry AK Saha SK Dempsey PW Cheng G 《Journal of immunology (Baltimore, Md. : 1950)》2005,174(3):1602-1607
Type I IFNs are well established antiviral cytokines that have also been shown to be induced by bacteria. However, the signaling mechanisms regulating the activation of these cytokines during bacterial infections remain poorly defined. We show that although Gram-negative bacteria can activate the type I IFN pathway through TLR4, the intracellular Gram-positive bacterium Listeria monocytogenes (LM) can do so independently of TLR4 and TLR2. Furthermore, experiments using genetic mutants and chemical inhibitors suggest that LM-induced type I IFN activation occurs by an intracellular pathway involving the serine-threonine kinase TNFR-associated NF-kappaB kinase (TANK)-binding kinase 1 (TBK1). Interestingly, receptor-interacting protein 2, a component of the recently discovered nucleotide-binding oligomerization domain-dependent intracellular detection pathway, was not involved. Taken together, our data describe a novel signal transduction pathway involving TBK1 that is used by LM to activate type I IFNs. Additionally, we provide evidence that both the LM- and TLR-dependent pathways converge at TBK1 to activate type I IFNs, highlighting the central role of this molecule in modulating type I IFNs in host defense and disease. 相似文献
148.
Mouse B16LuF1 melanoma cells of lower metastatic potential to lung were treated in vitro with same concentration (50 microM) of gangliosides prepared from plasma of mice bearing lung metastasis of B16LuF5, B16LuF9 or B16LuF10 melanoma cell lines of increasing metastatic potential to lung (LuF1 < LuF5 < LuF9 < LuF10) and injected to normal mice through tail vein. The number of metastatic tumor nodules formed in lung increased gradually in mice receiving B16LuF5, B16LuF9 and B16LuF10-ganglioside-treated B16LuF1 cells compared to mice receiving B16LuF1 cells without any ganglioside treatment. Similarly, mouse B16LuF1 melanoma cells treated in vitro with 50 microM concentration of gangliosides prepared from spent culture media of B16LuF5, B16LuF9 or B16LuF10 cells cultured in vitro were injected to normal mice through tail vein. The number of metastatic tumor nodules formed in lung increased gradually in mice receiving B16LuF5, B16LuF9 and B16LuF10-ganglioside-treated B16LuF1 cells compared to mice receiving B16LuF1 cells without any ganglioside treatment. The results indicated that metastasis-associated gangliosides present in plasma and culture media of B16-melanoma of increasing metastatic potential to lung enhanced metastatic potential of B16LuF1 cells. The increasing concentration of metastasis-associated gangliosides present in plasma and in culture media of B16-melanoma of increasing metastatic potential possibly determined increase in metastatic potential of B16LuF1-melanoma cells. 相似文献
149.
Saha PK Kojima H Martinez-Botas J Sunehag AL Chan L 《The Journal of biological chemistry》2004,279(34):35150-35158
150.
The pill is the most popular family planning method in Bangladesh. However, the failure rate of this method in Matlab, a typical rural area, has been found to be very high. It is estimated that with the current level of failure of the pill and other temporary contraceptives in Matlab, it is unlikely that fertility in Bangladesh will come down to replacement level without a change in contraceptive method mix. It is, therefore, important to know the reasons for the high failure in pill use. Data for this study came from a case-control study in Matlab. A pill failure was considered a case, and no-failure was considered a control. The study included 167 cases and 167 controls. In addition, five focus group discussions were conducted to supplement the data collected from the cases and controls to gain a deeper understanding of pill failure. Results of the analysis of both quantitative and qualitative data suggested that the following were the risk factors for pill failure: no mobility of women, poor knowledge of women about the effectiveness and consequences of drop-out from pill use, weak confidence in the pill, a gap between the use of subsequence pill cycles, delay in starting the pill after menstruation for the first use, not taking any measures consistently for missing the pill, and not following the arrow sign given on the pill cycle. Extensive training of field workers and pill users, covering the reasons for pill failure identified in this study and strong supervision of the work of field workers, is likely to reduce the rate of pill failure in Bangladesh. Also, information, education and communication services for users, and management of side-effects, may be helpful in reducing pill failure. 相似文献