全文获取类型
收费全文 | 47400篇 |
免费 | 3353篇 |
国内免费 | 19篇 |
专业分类
50772篇 |
出版年
2024年 | 52篇 |
2023年 | 175篇 |
2022年 | 565篇 |
2021年 | 912篇 |
2020年 | 568篇 |
2019年 | 682篇 |
2018年 | 1028篇 |
2017年 | 907篇 |
2016年 | 1477篇 |
2015年 | 2320篇 |
2014年 | 2666篇 |
2013年 | 2978篇 |
2012年 | 3941篇 |
2011年 | 3778篇 |
2010年 | 2392篇 |
2009年 | 2184篇 |
2008年 | 3028篇 |
2007年 | 2909篇 |
2006年 | 2540篇 |
2005年 | 2356篇 |
2004年 | 2162篇 |
2003年 | 1864篇 |
2002年 | 1614篇 |
2001年 | 1301篇 |
2000年 | 1228篇 |
1999年 | 990篇 |
1998年 | 393篇 |
1997年 | 338篇 |
1996年 | 245篇 |
1995年 | 209篇 |
1994年 | 207篇 |
1993年 | 172篇 |
1992年 | 326篇 |
1991年 | 295篇 |
1990年 | 266篇 |
1989年 | 226篇 |
1988年 | 173篇 |
1987年 | 163篇 |
1986年 | 131篇 |
1985年 | 105篇 |
1984年 | 78篇 |
1983年 | 84篇 |
1982年 | 63篇 |
1981年 | 53篇 |
1980年 | 54篇 |
1979年 | 69篇 |
1978年 | 51篇 |
1977年 | 50篇 |
1976年 | 43篇 |
1974年 | 63篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
Chronic amphetamine alters D-2 but not D-1 agonist-induced behavioral responses in rats 总被引:2,自引:0,他引:2
In two experiments, using different drug doses and periods of drug administration, rats were given amphetamine (AMPH) either continuously (via slow-release pellets), or intermittently (via injections). In both experiments, only the rats pretreated with intermittent AMPH subsequently showed heightened responsivity to the selective D-2 dopamine agonist LY171555 but not to SKF38393 (a D-1 agonist). This altered response to LY171555 was still present 30 days after the AMPH withdrawal, implying that D-2 dopamine receptors at least partially mediate AMPH inverse tolerance effects. The behavioral response to the D-2 agonist was clearly different in animals receiving high versus low doses of AMPH, suggesting that different drug-state learning may have occurred during pretreatment. In a third experiment, in which rats were given repeated daily injections of either the D-1 or the D-2 agonist, only rats pretreated with the D-2 agonist and subsequently injected with the D-2 agonist clearly showed heightened responsivity. These data imply an important role of D-2 receptors in the AMPH inverse tolerance effect. 相似文献
82.
Production and Characterization of Monoclonal Antibodies to Wall-Localized Peroxidases from Corn Seedlings 总被引:2,自引:1,他引:1
下载免费PDF全文
![点击此处可从《Plant physiology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Sung-Ha Kim Maurice E. Terry Pepper Hoops Marianne Dauwalder Stanley J. Roux 《Plant physiology》1988,88(4):1446-1453
A library of 22 hybridomas, which make antibodies to soluble wall antigens from the coleoptiles and primary leaves of etiolated corn (Zea mays L.) seedlings, was raised and cloned three times by limit dilution to assure monoclonal growth and stability. Two of these hybridomas made immunoglobulin G antibodies, designated mWP3 and mWP19, which both effectively immunoprecipitated peroxidase activity from crude and partially purified preparations of wall peroxidases. Direct peroxidase-binding assays revealed that both antibodies bound enzymes with peroxidase activity. As judged by immunoblot analyses, mWP3 recognized a Mr 98,000 wall peroxidase with an isoelectric point near 4.2, and mWP19 recognized a Mr 58,000 wall peroxidase. Immunogold localization studies showed both peroxidases are predominately in cell walls. 相似文献
83.
Physical interactions between pyridoxal kinase and aspartate aminotransferase were detected by means of emission anisotropy and affinity chromatography techniques. Binding of aspartate aminotransferase (apoenzymes) to pyridoxal kinase tagged with a fluorescent probe was detected by emission anisotropy measurements at pH 6.8 (150 mM KCl). Upon saturation of the kinase with the aminotransferase, the emission anisotropy increases 22%. The protein complex is characterized by a dissociation constant of 3 microM. Time-dependent emission anisotropy measurements conducted with the mixture 5-naphthylamine-1-sulfonic acid-kinase aspartate aminotransferase (apoenzyme), revealed the presence of two rotational correlation times of phi 1 = 36 and phi 2 = 62 ns. The longer correlation time is attributed to the stable protein complex. By immobilizing one enzyme (pyridoxal kinase) through interactions with pyridoxal-Sepharose, it was possible to demonstrate that aspartate aminotransferase releases pyridoxal kinase. A test of compartmentation of pyridoxal-5-phosphate within the protein complex using alkaline phosphatase as trapping agent, indicates that the cofactor generated by the catalytic action of the kinase is channeled to the apotransaminase. The main function of the stable complex formed by the kinase and the aminotransferase is to hinder the release of free pyridoxal-5-phosphate into the bulk solvent. 相似文献
84.
Ubiquitin genes in trypanosomatidae 总被引:11,自引:0,他引:11
L V Kirchhoff K S Kim D M Engman J E Donelson 《The Journal of biological chemistry》1988,263(25):12698-12704
85.
86.
Assessment of arterial-venous differences across transplanted methylcholanthrene-induced sarcomas in rats revealed significant decreases in plasma concentrations of glutamine, serine and glucose. Treatment with the glutamine antimetabolite, acivicin, significantly reduced tumor weights by 65% at the conclusion of the experiment 34 days after tumor induction. These results suggest that glutamine is an essential metabolic substrate for tumor growth and that blockade of glutamine utilization can inhibit the growth of these transplantable sarcomas. 相似文献
87.
Sodium-dependent lysine flux across bullfrog alveolar epithelium 总被引:2,自引:0,他引:2
Amino acid transport across the alveolar epithelial barrier was studied by measuring radiolabeled lysine fluxes across bullfrog lungs in an Ussing chamber. In the absence of a transmural electrical gradient, L-[14C]lysine was instilled into the upstream reservoir and the rate of appearance of the radiolabel in the downstream reservoir was determined. Two lungs from the same animal were used simultaneously to determine tracer fluxes both into and out of the alveolar bath. Results showed that the radiolabel flux measured in the alveolar to the pleural direction was greater than that measured in the opposite direction in the presence of sodium in the bathing fluids. The net flux of L-[14C]lysine was saturable with [Na+], with an apparent transport coefficient (Kt) of 28 mM for Na+. Hill analysis of [14C]lysine flux vs. [Na+] indicated a coupling ratio of 1:1 between sodium and radiolabeled L-lysine. Total L-lysine flux as a function of [L-lysine] was also saturable, with Kt of 7.3 mM for L-lysine. Ouabain significantly decreased absorptive (alveolar-to-pleural) radiolabel flux, while slightly increasing the flux observed in the opposite direction. L-leucine completely inhibited absorptive net flux of L-[14C]lysine. alpha-Methylaminoisobutyric acid (MeAIB), on the other hand, only slightly reduced net flux of L-[14C]lysine from the control value. The presence of a net absorptive, Na+-dependent amino acid flux across the alveolar epithelial barrier indicates that the tissue is capable of removing amino acids and sodium from the alveolar fluid by a coupled cotransport mechanism, which may be important for both protein metabolism and fluid balance by alveolar epithelium. 相似文献
88.
K H Kim H Takeuchi E Munekata N Yanaihara Y Ariyoshi 《Comp. Biochem. Physiol. C, Comp. Pharmacol. Toxicol.》1988,91(2):549-552
1. Effects of the following peptides at 10(-4) M on identifiable giant neurones of Achatina fulica Férussac were examined: physalaemin, eledoisin, bradykinin, neurokinin A, neurokinin B, neuromedin B, gastrin releasing peptide decapeptide (neuromedin C), gastrin releasing peptide (14-27), cholecystokinin tetrapeptide, cholecystokinin octapeptide, thyrotropin releasing hormone, Arg-vasotocin, gamma-melanocyte stimulating hormone. 2. The six neurones tested were as follows: PON (periodically oscillating neurone), TAN (tonically autoactive neurone), RAPN (right anterior pallial neurone), d-RPLN (dorsal-right parietal large neurone), VIN (visceral intermittently firing neurone) and d-VLN (dorsal-visceral large neurone). 3. Of the peptides examined, only Arg-vasotocin at 10(-4) M produced the excitatory effects on PON, VIN and d-VLN. Physalaemin showed slight inhibitory effects on TAN; this substance was sometimes almost ineffective on the neurone. 4. The other peptides examined were completely ineffective on all of the neurones tested. 相似文献
89.
K Leung K E Kim R A Maurer T D Landefeld 《Molecular endocrinology (Baltimore, Md.)》1988,2(3):272-276
Cyclic changes in the production of the pituitary gonadotrophic hormones, LH and FSH are essential events in the maintenance of the reproductive system of female mammals. While studies have examined changes in the secretion of LH and FSH during the estrous cycle and demonstrated the importance of these hormones in regulation of ovarian development and gametogenesis, considerably less is known concerning the regulation of the biosynthesis of these hormones. Although initial studies have examined changes in LH subunit mRNA concentrations during the rat and ovine estrous cycles, no information concerning the physiological regulation of FSH beta mRNA concentrations has been available. In the present study we have examined the relationship between pituitary concentrations of LH and FSH subunit mRNAs and the serum concentrations of these gonadotropins. The results demonstrate a very different pattern of change for FSH beta subunit mRNA than that observed for alpha and LH beta subunit mRNAs. In fact, FSH beta mRNA concentration decline substantially during the preovulatory period, reaching minimal values at a time when alpha and LH beta mRNA levels are near maximal. Furthermore, this decline in FSH beta mRNA amounts occurs when serum FSH concentrations are maximal. Thus, FSH beta mRNA concentrations follow a very different pattern than that of serum FSH. In contrast, LH beta mRNA and serum LH concentrations tend to increase at the same time. These findings provide evidence that concentrations of LH beta and FSH beta mRNAs are likely regulated by different mechanisms. 相似文献
90.
David Mulcahy Christine Wright Lorna Mockus Magdi Yacoub Kim Fox 《BMJ (Clinical research ed.)》1988,296(6625):817-819
Sixty four patients were referred for cardiac transplantation from a single cardiac team at this hospital between October 1984 and December 1986. Of these patients, 33 were referred for urgent transplantation, all of whom required intensive treatment in hospital with intravenous infusions of cardiac drugs, intra-aortic balloon counterpulsation, peritoneal dialysis, ventilation, or any combination of these to sustain life. Of these 33 patients, six died while awaiting transplantation, one was removed from the waiting list for a transplant, and 26 received cardiac transplants. There were five deaths within 24 hours of operation and one death 10 days after the operation. Twenty of those who had surgery had a successful outcome of transplantation, but there was one late death 10 weeks postoperatively and a further death 31 months after surgery. Eighteen patients were alive and well 10 to 33 months (mean 19·4 months) after transplantation, with an overall survival rate after surgery of 69%.Provided that surgery can be performed before renal failure has progressed such that renal transplantation is necessary, the results are excellent (surgical survival 85·5%) and, we believe, justify the expenditure and staffing requirements necessary to treat these terminally ill patients. 相似文献