全文获取类型
收费全文 | 11688篇 |
免费 | 830篇 |
国内免费 | 2篇 |
出版年
2023年 | 119篇 |
2022年 | 195篇 |
2021年 | 427篇 |
2020年 | 311篇 |
2019年 | 397篇 |
2018年 | 451篇 |
2017年 | 412篇 |
2016年 | 542篇 |
2015年 | 709篇 |
2014年 | 737篇 |
2013年 | 834篇 |
2012年 | 950篇 |
2011年 | 839篇 |
2010年 | 528篇 |
2009年 | 452篇 |
2008年 | 552篇 |
2007年 | 522篇 |
2006年 | 454篇 |
2005年 | 397篇 |
2004年 | 366篇 |
2003年 | 334篇 |
2002年 | 285篇 |
2001年 | 212篇 |
2000年 | 188篇 |
1999年 | 163篇 |
1998年 | 52篇 |
1997年 | 62篇 |
1996年 | 47篇 |
1995年 | 35篇 |
1994年 | 43篇 |
1993年 | 41篇 |
1992年 | 88篇 |
1991年 | 62篇 |
1990年 | 49篇 |
1989年 | 59篇 |
1988年 | 51篇 |
1987年 | 63篇 |
1986年 | 47篇 |
1985年 | 45篇 |
1984年 | 47篇 |
1983年 | 23篇 |
1982年 | 24篇 |
1981年 | 23篇 |
1979年 | 33篇 |
1978年 | 18篇 |
1977年 | 15篇 |
1976年 | 20篇 |
1975年 | 27篇 |
1974年 | 19篇 |
1973年 | 28篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
141.
Summary A large pedigree with a satellited Yq chromosome is described, Q, C, and NOR banding were performed. Family C proband suffers from a Klinefelter syndrome. 相似文献
142.
J.A.F. de Silva 《Journal of chromatography. B, Analytical technologies in the biomedical and life sciences》1983,273(1):19-42
Therapeutic drug monitoring can involve quantitation in either microgram, nanogram or picogram concentrations present in a complex biological matrix (whole blood, urine or tissue).The chemical structure of a compound influences not only the analytical method best suited to its quantitation, but also its acid/base character (PKa) and its extractability. The dose administered, the bioavailability of the dosage form, and the pharmacokinetic profile of the drug govern the circulating concentrations of either the parent drug and/or its metabolites present in vivo, and dictate the ultimate sensitivity and specificity required of the analytical method.The degree of sample preparation required is dependent on the analytical method used (gas—liquid chromatography, thin-layer chromatography, high-performance liquid chromatography) and on the tolerance of the specific type of detection system to contamination. Factors leading to compound losses during sample preparation (adsorption, stability) are critical at low concentrations and can adversely affect the reliability of an assay, therefore maximizing the overall recovery of the assay is essential not only for high sensitivity but also for good precision and accuracy. Therefore, the criteria to be used in sample preparation should aim to optimize all of the above factors in the overall development of a reliable and validated method for the compound suitable for use in clinical therapeutic monitoring. 相似文献
143.
144.
F. M. J. Heemskerk L. H. Schrama W. E. J. M. Ghijsen P. N. E. De Graan F. H. Lopes da Silva W. H. Gispen 《Journal of neurochemistry》1991,56(6):1827-1835
Abstract: Recently we have shown that 4-aminopyridine (4-AP), a drug known to enhance transmitter release, stimulates the phosphorylation of the protein kinase C substrate B-50 (GAP-43) in rat brain synaptosomes and that this effect is dependent on the presence of extracellular Ca2+ . Hence, we were interested in the relationship between changes induced by 4-AP in the intracellular free Ca2+ concentration ([Ca2+ ]i ) and B-50 phosphorylation in synaptosomes. 4-AP (100 μ M ) elevates the [Ca2+ ]i (as determined with fura-2) to approximately the same extent as depolarization with 30 m M K+ (from an initial resting level of 240 n M to ∼480 n M after treatment). However, the underlying mechanisms appear to be different: In the presence of 4-AP, depolarization with K+ still evoked an increase in [Ca2+ ]i , which was additive to the elevation caused by 4-AP. Several Ca2+ channel antagonists (CdCl2 , LaCl3 , and diphenylhydantoin) inhibited the increase in B-50 phosphorylation by 4-AP. It is interesting that the increase in [Ca2+ ]i and the increase in B-50 phosphorylation by 4-AP were attenuated by tetrodotoxin, a finding pointing to a possible involvement of Na+ channels in this action. These results suggest that 4-AP (indirectly) stimulates both Ca2+ influx and B-50 phosphorylation through voltage-dependent channels by a mechanism dependent on Na+ channel activity. 相似文献
145.
Calcium binding to proteins containing the 'EF-hand' structural motif regulates a variety of biochemical processes including muscle contraction. Techniques such as protein crystallography, site-directed mutagenesis and domain transplantation experiments are being used to unravel the conformational changes induced by calcium binding. 相似文献
146.
Wim E. J. M. Ghijsen Elly Besselsen Vincent Geukers Willem Kamphuis Fernando H. Lopes da Silva 《Journal of neurochemistry》1992,59(2):482-486
The effect of long-term potentiation (LTP) on endogenous amino acid release from rat hippocampus slices was studied. LTP was induced in vivo by application of a tetanus (200 Hz, 200 ms) to the Schaffer collateral fibers in unanesthetized rats. Endogenous release of glutamate and gamma-aminobutyric acid (GABA) was investigated 60 min after tetanization in CA1 subslices of potentiated and control rats. No significant effects of LTP were observed in basal and K(+)-induced Ca(2+)-independent release components of these amino acids. In contrast, K(+)-induced Ca(2+)-dependent release of both glutamate and GABA increased approximately 100% in slices from potentiated rats. No differences were observed in total content of glutamate and GABA between the subslices from control and LTP animals. These results suggest a persistent increase in the recruitment of the presynaptic vesicular pool of glutamate and GABA during LTP. 相似文献
147.
Effects of hydrostatic pressure on a membrane-enveloped virus: high immunogenicity of the pressure-inactivated virus. 总被引:9,自引:0,他引:9
下载免费PDF全文
![点击此处可从《Journal of virology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
A new approach to the preparation of antiviral vaccines relying on the inactivation of the virus particle by hydrostatic pressure is described. The enveloped virus vesicular stomatitis virus was utilized as a model; a pressure of 260 MPa applied for 12 h reduced infectivity by a factor of 10(4), and the antibodies against pressurized material were as effective as those against the intact virus when measured by their neutralization titer. Fluorescence measurements indicate that application of pressure results in perturbations of the particle interactions that permit binding of specific molecular probes. Electron microscopy showed that the membrane of the pressurized virus was partially preserved, presenting the spike pattern of the membrane G protein. Unlike the icosahedral viruses, dissociation into smaller particles was not observed, but a constant change in the morphology was the presence of a bulge in the surface of the pressurized virus, indicating a displacement of the capsid subunits, retained under the lipid and protein membrane. 相似文献
148.
149.
Summary The optimum conditions forAcetobacter immobilization were investigated. The results show that: 1) the maximum oxygen uptake rate (OURm) and cell release are related to alginate and cell concentration in the gel; 2)different alginate concentration does not affect cell viability, but long storage in CaCl2 reduces the number of living cells; 3)the double alginate gel layers had no influence on cell viability and on the OURm and prevented cell leakage from the gel matrix. 相似文献
150.
After a 4-6 h induction period, insulin or progesterone induces Xenopus oocytes to enter prophase of meiosis. During the period of induction, both insulin and progesterone induced an increase in 32PO4 labeling of phosphatidylcholine and phosphatidylinositol. Through a mass assay, we found that insulin and progesterone increase inositol 1,4,5-trisphosphate (IP3) at about 15-30 s, 15 min and at about 2-3 h (0.5 GVBD50) after hormone addition. Since IP3 increases were small (from a basal of 66 to 104 nM), the results agree with prior conclusions that progesterone does not induce a large, cytosolic calcium elevation. Insulin is probably acting through the insulin-like growth factor-1 receptor as insulin concentrations greater than about 50 nM are required to increase IP3. 相似文献