全文获取类型
收费全文 | 3248篇 |
免费 | 216篇 |
国内免费 | 1篇 |
出版年
2022年 | 12篇 |
2021年 | 29篇 |
2020年 | 12篇 |
2019年 | 18篇 |
2018年 | 42篇 |
2017年 | 38篇 |
2016年 | 55篇 |
2015年 | 99篇 |
2014年 | 121篇 |
2013年 | 175篇 |
2012年 | 184篇 |
2011年 | 182篇 |
2010年 | 107篇 |
2009年 | 117篇 |
2008年 | 192篇 |
2007年 | 186篇 |
2006年 | 170篇 |
2005年 | 173篇 |
2004年 | 199篇 |
2003年 | 191篇 |
2002年 | 216篇 |
2001年 | 85篇 |
2000年 | 71篇 |
1999年 | 78篇 |
1998年 | 56篇 |
1997年 | 38篇 |
1996年 | 20篇 |
1995年 | 31篇 |
1994年 | 26篇 |
1993年 | 31篇 |
1992年 | 63篇 |
1991年 | 40篇 |
1990年 | 29篇 |
1989年 | 34篇 |
1988年 | 42篇 |
1987年 | 19篇 |
1986年 | 15篇 |
1985年 | 30篇 |
1984年 | 31篇 |
1983年 | 16篇 |
1982年 | 23篇 |
1981年 | 23篇 |
1980年 | 9篇 |
1979年 | 17篇 |
1978年 | 10篇 |
1976年 | 14篇 |
1975年 | 14篇 |
1974年 | 10篇 |
1972年 | 11篇 |
1970年 | 12篇 |
排序方式: 共有3465条查询结果,搜索用时 335 毫秒
241.
242.
Kimura M Hasegawa Y Nakagawa K Kajita M Watanabe K Yamaguchi S 《Journal of chromatography. B, Analytical technologies in the biomedical and life sciences》2003,792(1):141-144
4-Hydroxybutyric acid (4HB) was analyzed by gas chromatography-mass spectrometry. Under acidified conditions, 4HB is difficult to detect due to lactonization. Using a urine sample containing 0.01 mg creatinine, we performed trimethylsilyl derivatization without extraction, only adding dimethylsuccinic acid as an internal standard and 10 microl of 0.1 N NaOH methanol solution with adequate evaporation. Urine 4HB levels in a patient with 4-hydroxybutyric aciduria was determined to be 1258 mmol/mol Cr (control, 0.28-2.81 mmol/mol Cr) in this method. Direct derivatization of samples without extraction showed good reproducibility and linearity. Only a small sample of urine was required. Alkalinization by NaOH prevented not only lactonization of 4HB, but also loss of the compounds during evaporation. 相似文献
243.
Determination of polycyclic aromatic hydrocarbons in milk samples by high-performance liquid chromatography with fluorescence detection 总被引:1,自引:0,他引:1
Kishikawa N Wada M Kuroda N Akiyama S Nakashima K 《Journal of chromatography. B, Analytical technologies in the biomedical and life sciences》2003,789(2):257-264
This paper describes a high-performance liquid chromatographic (HPLC) method for the determination of polycyclic aromatic hydrocarbons (PAHs) in milk samples. The method involves a liquid-liquid extraction procedure after saponification of milk samples with sodium hydroxide. Reproducible determination with highly sensitive detection was attained by HPLC with fluorescence detection using 1,2-bis(9-anthryl)ethane as an internal standard. The detection limits of 12 kinds of PAHs ranged from 1.3 to 76 ng/kg milk at a signal/noise ratio of 3. By the proposed method, the presence of 12 and 11 kinds of PAHs could be confirmed in commercial milk and human milk samples, respectively. The average concentrations of total PAHs (mean+/-SD, micro g/kg) were found to be 0.99+/-0.37 for commercial milk (n=14), 2.01+/-0.30 for infant formula (n=3) and 0.75+/-0.47 for human milk (n=51). High correlation coefficients between the concentrations of total PAHs and triglyceride were observed for commercial milk (r=0.659) and human milk (r=0.645). 相似文献
244.
Interaction between leukemic-cell VLA-4 and stromal fibronectin is a decisive factor for minimal residual disease of acute myelogenous leukemia 总被引:27,自引:0,他引:27
Matsunaga T Takemoto N Sato T Takimoto R Tanaka I Fujimi A Akiyama T Kuroda H Kawano Y Kobune M Kato J Hirayama Y Sakamaki S Kohda K Miyake K Niitsu Y 《Nature medicine》2003,9(9):1158-1165
Bone-marrow minimal residual disease (MRD) causes relapse after chemotherapy in patients with acute myelogenous leukemia (AML). We postulate that the drug resistance is induced by the attachment of very late antigen (VLA)-4 on leukemic cells to fibronectin on bone-marrow stromal cells. We found that VLA-4-positive cells acquired resistance to anoikis (loss of anchorage) or drug-induced apoptosis through the phosphatidylinositol-3-kinase (PI-3K)/AKT/Bcl-2 signaling pathway, which is activated by the interaction of VLA-4 and fibronectin. This resistance was negated by VLA-4-specific antibodies. In a mouse model of MRD, we achieved a 100% survival rate by combining VLA-4-specific antibodies and cytosine arabinoside (AraC), whereas AraC alone prolonged survival only slightly. In addition, overall survival at 5 years was 100% for 10 VLA-4-negative patients and 44.4% for 15 VLA-4-positive patients. Thus, the interaction between VLA-4 on leukemic cells and fibronectin on stromal cells may be crucial in bone marrow MRD and AML prognosis. 相似文献
245.
Kawao N Hiramatsu K Inoi N Kuroda R Nishikawa H Sekiguchi F Kawabata A 《Peptides》2003,24(9):1449-1451
Protease-activated receptor-2 (PAR-2) is abundantly expressed in gastric mucosal chief cells, facilitating pepsinogen secretion. In the present study, we investigated whether PAR-1, a thrombin receptor, could modulate pepsinogen secretion in rats. The PAR-1-activating peptide TFLLR-NH(2) as well as the PAR-2-activating peptide SLIGRL-NH(2), administered i.v. repeatedly at 1-h intervals, significantly increased gastric pepsinogen secretion over 2-4 h (after two to four doses). In contrast, the control peptide FTLLR-NH(2), given in the same manner, had no such effect. Thus, PAR-1, like PAR-2, might function to facilitate pepsinogen secretion, suggesting a novel role of the thrombin-PAR-1-pathway in the stomach. 相似文献
246.
Review of sarcomatoid renal cell carcinoma with focus on clinical and pathobiological aspects 总被引:2,自引:0,他引:2
In sarcomatoid renal cell carcinoma (RCC), it is generally accepted that the sarcomatoid portion is derived from metaplastic transformation of carcinoma. Sarcomatoid RCCs account for about 1-8% of all renal tumors. Macroscopically, tumors generally form encapsulated masses and show invasive growth. Sarcomatoid RCCs originate from all subtypes of RCCs, including conventional, papillary, chromophobe, and collecting duct carcinomas. With regard to the growth pattern of the sarcomatoid component, malignant fibrous histiocytomatous, fibrosarcomatous and unclassified sarcomatous patterns are frequently seen. Immunohistochemically, sarcomatoid RCCs are generally positive for AE1/AE3, epithelial membrane antigen (EMA) and vimentin and negative for desmin, actin and S-100. Little is know about genetic alterations in sarcomatoid RCCs. Further studies are therefore needed to identify the key gene involved in sarcomatoid transformation of RCCs. 相似文献
247.
Masahiko?HirataEmail author Mihoko?Nakagawa Harumi?Funakoshi Takuya?Iwamoto Waka?Otozu Daisuke?Kiyota Shirou?Kuroki Kiichi?Fukuyama 《Journal of Ethology》2003,21(2):161-168
Distance between dam and offspring (1–121 days old) in a herd of Japanese Black cattle (Bos taurus) grazing a tropical grass (Paspalum notatum) pasture (1.5 ha) was investigated during 7-h grazing periods over grazing seasons from May (spring) to October (autumn).
The mother–young distance was not constant throughout the grazing period, repeatedly increasing and decreasing. Although significant
periodicity was always detected in the mother–young distance, there was no consistent dominant cycle, indicating the complexity
of the within-day pattern of mother–young distance. The mean mother–young distance over the grazing period increased as a
calf aged, reaching a plateau at an age of about 33 days. The mean distance of a calf from its mother was usually shorter
than that from a non-mother cow, with the difference between the mean distances decreasing sharply until a calf became about
35 days old. The results and literature show that mutual independence of mother and young rapidly develops in the first 30–50 days
after parturition.
Electronic Publication 相似文献
248.
We examined the effects of radiation on decreases in osteoclast numbers after regional irradiation of rats with carbon ions and gamma rays. Male Wistar rats were subjected to hind-leg irradiation with carbon ions (290 MeV/u) or gamma rays at doses of 15, 22.5, or 30 Gy. The effects of carbon ions and gamma rays on osteoclasts were studied using histologic and morphometric methods. At doses of 15 Gy and 22.5 Gy, osteoclast numbers increased transiently until day 5 after irradiation and then decreased rapidly in both the carbon ion and gamma ray irradiation groups. The carbon ion group showed reduced osteoclast size compared with the gamma ray group. Carbon ion irradiation had a more marked effect on osteoclast activity, and suppressed maturation to a greater extent than gamma irradiation. These observations suggest that carbon ion irradiation induces differential modulation of osteoclast growth factor expression. 相似文献
249.
In the present study, the effect of constituting amino acid residue numbers of oligopeptide derivatives, which are candidate materials to construct molecular recognition sites, on chiral recognition ability was investigated. Chiral recognition sites were formed from oligopeptide derivatives, of which constituting amino acid residue numbers were three to six, by adopting an alternative molecular imprinting. It was made clear that the number four, in other words, the tetrapeptide derivative, is the best candidate material to form a chiral recognition site. 相似文献
250.
Characterization of factors involved in the production of 2(E)-nonenal during mashing 总被引:1,自引:0,他引:1
Kuroda H Furusho S Maeba H Takashio M 《Bioscience, biotechnology, and biochemistry》2003,67(4):691-697
To characterize the factors involved in the production of volatile aldehydes during mashing, a model mashing experiment was done. After we inactivated the endogenous lipoxygenase (LOX) activity in the mash by mashing at 70 degrees C for 30 min, further incubation with recombinant barley LOX-1 stimulated the accumulation of 2(E)-nonenal; however, this effect was significantly reduced by boiling the mash sample. The result suggests that both LOX-1 and a heat-stable enzymatic factor are involved in the production of 2(E)-nonenal during mashing. Malt contained fatty acid hydroperoxide lyase-like activity (HPL-like activity) that transformed 9-hydroperoxy-10(E), 12(Z)-octadecadienoic and 13-hydroperoxy-9(Z), 11(E)-octadecadienoic acid into 2(E)-nonenal and hexanal, respectively. Proteinase K sensitivity tests showed that they are distinct factors. 9-HPL-like activity survived through the mashing at 70 degrees C for 30 min but was inactivated by boiling, suggesting it will be the heat-stable enzymatic factor found in the model mashing experiment. 相似文献