全文获取类型
收费全文 | 18365篇 |
免费 | 1741篇 |
国内免费 | 3036篇 |
出版年
2024年 | 26篇 |
2023年 | 297篇 |
2022年 | 463篇 |
2021年 | 1106篇 |
2020年 | 900篇 |
2019年 | 1020篇 |
2018年 | 886篇 |
2017年 | 658篇 |
2016年 | 914篇 |
2015年 | 1386篇 |
2014年 | 1597篇 |
2013年 | 1657篇 |
2012年 | 2006篇 |
2011年 | 1792篇 |
2010年 | 1130篇 |
2009年 | 1080篇 |
2008年 | 1132篇 |
2007年 | 903篇 |
2006年 | 816篇 |
2005年 | 666篇 |
2004年 | 537篇 |
2003年 | 488篇 |
2002年 | 371篇 |
2001年 | 237篇 |
2000年 | 201篇 |
1999年 | 193篇 |
1998年 | 101篇 |
1997年 | 73篇 |
1996年 | 74篇 |
1995年 | 77篇 |
1994年 | 47篇 |
1993年 | 37篇 |
1992年 | 46篇 |
1991年 | 41篇 |
1990年 | 27篇 |
1989年 | 28篇 |
1988年 | 12篇 |
1987年 | 20篇 |
1986年 | 15篇 |
1985年 | 18篇 |
1984年 | 10篇 |
1983年 | 12篇 |
1982年 | 10篇 |
1981年 | 3篇 |
1977年 | 3篇 |
1975年 | 5篇 |
1974年 | 3篇 |
1973年 | 3篇 |
1969年 | 2篇 |
1964年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
22.
Rhida M'Rad Marek Sanak Georges Deschenes Jing Zhou Catherine Bonaiti-Pellie Laurent Holvoet-Vermaut Solange Heuertz Marie-Claire Gubler Michel Broyer Jean-Pierre Grunfeld Karl Tryggvason Marie-Claude Hors-Cayla 《Human genetics》1992,90(4):420-426
Thirty one families with Alport syndrome including 3 families with associated syndromes were studied. The location of the COL4A5 gene, responsible for the Alport syndrome, was determined by linkage analysis with eight probes of the Xq arm and by a radiation hybrid panel. Concordant data indicated the localization of the Alport gene between DXS17 and DXS11. Four deletions and one single base mutation of the COL4A5 gene were detected. Homogeneity tests failed to show any evidence of genetic heterogeneity superimposed on clinical heterogeneity for ophthalmic signs and end-stage renal disease age. 相似文献
23.
磁场对大豆共生固氮的效应 总被引:1,自引:0,他引:1
恒定磁场处理慢生大豆根瘤菌“005”和接种后的大豆植株,发现磁场可以提高根瘤的固氮活性。在一定的磁场强度(70—100mT)下,固氮活性平均可以提高4—5倍,植株的结瘤数和根瘤重量平均提高2—3倍。从这样的根瘤中所分离出的根瘤菌,由慢生型转变成快生型,在100植株中有17株的根瘤分离出快生菌。生长世代时间和培养溶液中的pH值与慢生型不同,而与快生型相同。 相似文献
24.
The trk tyrosine protein kinase mediates the mitogenic properties of nerve growth factor and neurotrophin-3. 总被引:45,自引:0,他引:45
C Cordon-Cardo P Tapley S Q Jing V Nanduri E O'Rourke F Lamballe K Kovary R Klein K R Jones L F Reichardt 《Cell》1991,66(1):173-183
The product of the trk proto-oncogene encodes a receptor for nerve growth factor (NGF). Here we show that NGF is a powerful mitogen that can induce resting NIH 3T3 cells to enter S phase, grow in semisolid medium, and become morphologically transformed. These mitogenic effects are absolutely dependent on expression of gp140trk receptors, but do not require the presence of the previously described low affinity NGF receptor. gp140trk also serves as a receptor for the related factor neurotrophin-3 (NT-3), but not for brain-derived neurotrophic factor. Both NGF and NT-3 induce the rapid phosphorylation of gp140trk receptors and the transient expression of c-Fos proteins. However, NT-3 appears to elicit more limited mitogenic responses than NGF. These results indicate that the product of the trk proto-oncogene is sufficient to mediate signal transduction processes induced by NGF and NT-3, at least in proliferating cells. 相似文献
25.
The trkB tyrosine protein kinase is a receptor for brain-derived neurotrophic factor and neurotrophin-3. 总被引:48,自引:0,他引:48
R Klein V Nanduri S A Jing F Lamballe P Tapley S Bryant C Cordon-Cardo K R Jones L F Reichardt M Barbacid 《Cell》1991,66(2):395-403
trkB is a tyrosine protein kinase gene highly related to trk, a proto-oncogene that encodes a receptor for nerve growth factor (NGF) and neurotrophin-3 (NT-3). trkB expression is confined to structures of the central and peripheral nervous systems, suggesting it also encodes a receptor for neurotrophic factors. Here we show that brain-derived neurotrophic factor (BDNF) and NT-3, but not NGF, can induce rapid phosphorylation on tyrosine of gp145trkB, one of the receptors encoded by trkB. BDNF and NT-3 can induce DNA synthesis in quiescent NIH 3T3 cells that express gp145trkB. Cotransfection of plasmids encoding gp145trkB and BDNF or NT-3 leads to transformation of recipient NIH 3T3 cells. In these assays, BDNF elicits a response at least two orders of magnitude higher than NT-3. Finally, 125I-NT-3 binds to NIH 3T3 cells expressing gp145trkB; binding can be competed by NT-3 and BDNF but not by NGF. These findings indicate that gp145trkB may function as a neurotrophic receptor for BDNF and NT-3. 相似文献
26.
The trk proto-oncogene encodes a receptor for nerve growth factor. 总被引:127,自引:0,他引:127
Two classes of receptors with distinct affinities for nerve growth factor (NGF) have been identified. The low affinity receptor (Kd approximately 10(-9) to 10(-8) M) is a cysteine-rich glycoprotein encoded by the previously characterized LNGFR gene. The structural nature of the high affinity receptor (Kd approximately 10(-11) to 10(-10) M) has yet to be established. In this study we show that the product of the human trk proto-oncogene (gp140trk) binds NGF with high affinity. Moreover, NGF could be chemically cross-linked to the endogenous gp140trk present in rat PC12 pheochromocytoma cells as well as to gp140trk ectopically expressed in mouse fibroblasts and in insect Sf9 cells. High affinity binding of NGF to gp140trk can occur in the absence of low affinity LNGFR receptors, at least in nonneural cells. Addition of NGF to PC12 cells elicits rapid phosphorylation of gp140trk on tyrosine residues and stimulates its tyrosine kinase activity. These results indicate that gp140trk is a functional NGF receptor that mediates at least some of the signal transduction processes initiated by this neurotrophic factor. 相似文献
27.
本文对高胆固醇血症家兔红细胞在交、直流电场中的电泳行为进行了多指标测定,结果显示,高脂组与正常组相比红细胞聚集能力增强,变形能力及膜流动性下降,表明高脂血症可能较易导致血栓形成。中药有效成分8501有对抗高脂引起的红细胞上述改变的作用,提示8501可能对血栓和动脉粥样硬化斑块形成有防治作用。 相似文献
28.
The effects of centrally administered kentsin (H-Thr-Pro-Arg-Lys-OH) on intestinal motility and on pain perception were investigated in rats chronically equipped with lateral ventricle catheters. Intestinal motility was recorded electromyographically from electrodes placed on the duodeno-jejunum; analgesia was evaluated by the hot-plate and tail-flick tests. Kentsin (4.0 ug/kg), injected intracerebroventricularly (ICV) 2 hours after the beginning of a meal, restores the "fasted" i.e. the migrating myoelectric complex of intestinal motility, while a 5 times higher dose administered subcutaneously was inactive. The ICV effect of kentsin was blocked by previous ICV administration of naloxone (400 ug/kg). In contrast, kentsin administered ICV (40 ug/kg) or SC (200 ug/kg) did not affect significantly (P greater than 0.05) the time latency in the two analgesic tests during 90 minutes after its administration and did not significantly modify the analgesic effects of (D5-Ala2, Met5) enkephalinamide. We conclude that kentsin when centrally administered acts on opiate receptors to alter gastrointestinal motility but without effects on pain perception. 相似文献
29.
These experiments in the slowly adapting stretch receptor of crayfish test the effects of brief length perturbations (i.e., pulses) when presented in isolation at different constant elongations or superimposed on trapezoidal stretches of different amplitudes. Within "in vivo" lengths, during static responses, perturbations reduced firing rates to below control values and, in extreme cases, could silence the receptor. This effect, or "down-step," was sustained, occurred above a threshold pulse amplitude and background stretch, and increased with both stimulus characteristics, but was not present during dynamic responses. Beyond "in vivo" lengths, and in a few cases within those limits but close to the extremes, the receptor was silent but perturbations could restore activity. Lengthening pulses were more effective than shortening ones in generating after-effects. Perturbations change, during indefinitively long periods, the receptor's length or static sensitivity acting as a negative feedback which tends to maintain the discharge rate within fixed values. Perturbations disclose marked nonlinearities, which suggest that the classical view of a proportional control in the reflex loop in which the receptor participates may not operate in natural conditions. 相似文献
30.
Differentiated pressor and sympathetic responses to dual brain stimulation: ventromedial hypothalamus versus locus coeruleus 总被引:1,自引:0,他引:1
R D Bu?ag A Inoue 《Proceedings of the Society for Experimental Biology and Medicine. Society for Experimental Biology and Medicine (New York, N.Y.)》1985,178(1):91-100
Sensitivity of the ventromedial hypothalamus (VMH) to electrical stimulation was compared with that of the locus coeruleus (LC) in urethane-anesthetized rats. Based not only on current strengths required to elicit threshold effects, but also on magnitude of pressor responses to suprathreshold stimulation, the LC was consistently more sensitive than the VMH. Despite this greater pressor sensitivity, splanchnic nerve firing increased almost equally upon stimulation of either brain area. Similar comparisons made in other rats following bilateral adrenalectomy or pretreatment with a vasopressin antagonist showed no significant alteration of pressor and sympathetic responsiveness to stimulation of either the LC or the VMH. When frequency of neural firing was recorded from a lumbar sympathetic trunk instead of the splanchnic nerve, increases in sympathetic nerve activity produced by LC stimulation were significantly larger than those produced from the VMH. The results suggest that greater pressor sensitivity of the LC is due, at least in part, to stronger constriction in vascular beds innervated by the lumbar sympathetic chains. 相似文献