全文获取类型
收费全文 | 42417篇 |
免费 | 3925篇 |
国内免费 | 4672篇 |
出版年
2024年 | 97篇 |
2023年 | 573篇 |
2022年 | 1231篇 |
2021年 | 2205篇 |
2020年 | 1560篇 |
2019年 | 1917篇 |
2018年 | 1836篇 |
2017年 | 1366篇 |
2016年 | 1807篇 |
2015年 | 2719篇 |
2014年 | 3288篇 |
2013年 | 3413篇 |
2012年 | 4084篇 |
2011年 | 3695篇 |
2010年 | 2334篇 |
2009年 | 2170篇 |
2008年 | 2436篇 |
2007年 | 2182篇 |
2006年 | 1855篇 |
2005年 | 1566篇 |
2004年 | 1375篇 |
2003年 | 1294篇 |
2002年 | 1105篇 |
2001年 | 740篇 |
2000年 | 663篇 |
1999年 | 558篇 |
1998年 | 370篇 |
1997年 | 335篇 |
1996年 | 312篇 |
1995年 | 216篇 |
1994年 | 261篇 |
1993年 | 158篇 |
1992年 | 199篇 |
1991年 | 155篇 |
1990年 | 148篇 |
1989年 | 104篇 |
1988年 | 101篇 |
1987年 | 66篇 |
1986年 | 56篇 |
1985年 | 93篇 |
1984年 | 58篇 |
1983年 | 45篇 |
1982年 | 45篇 |
1981年 | 14篇 |
1979年 | 13篇 |
1978年 | 18篇 |
1974年 | 14篇 |
1973年 | 14篇 |
1971年 | 12篇 |
1965年 | 14篇 |
排序方式: 共有10000条查询结果,搜索用时 250 毫秒
41.
42.
Tissue plasminogen activator (tPA) has been implicated in neurite outgrowth and neurological recovery post stroke. tPA converts the zymogen plasminogen (Plg) into plasmin. In this study, using plasminogen knockout (Plg-/-) mice and their Plg-native littermates (Plg+/+), we investigated the role of Plg in axonal remodeling and neurological recovery after stroke. Plg+/+ and Plg-/- mice (n = 10/group) were subjected to permanent intraluminal monofilament middle cerebral artery occlusion (MCAo). A foot-fault test and a single pellet reaching test were performed prior to and on day 3 after stroke, and weekly thereafter to monitor functional deficit and recovery. Biotinylated dextran amine (BDA) was injected into the left motor cortex to anterogradely label the corticospinal tract (CST). Animals were euthanized 4 weeks after stroke. Neurite outgrowth was also measured in primary cultured cortical neurons harvested from Plg+/+ and Plg-/- embryos. In Plg+/+ mice, the motor functional deficiency after stroke progressively recovered with time. In contrast, recovery in Plg-/- mice was significantly impaired compared to Plg+/+ mice (p<0.01). BDA-positive axonal density of the CST originating from the contralesional cortex in the denervated side of the cervical gray matter was significantly reduced in Plg-/- mice compared with Plg+/+ mice (p<0.05). The behavioral outcome was highly correlated with the midline-crossing CST axonal density (R2>0.82, p<0.01). Plg-/- neurons exhibited significantly reduced neurite outgrowth. Our data suggest that plasminogen-dependent proteolysis has a beneficial effect during neurological recovery after stroke, at least in part, by promoting axonal remodeling in the denervated spinal cord. 相似文献
43.
44.
45.
本文选择两种溶剂体系,用两次单向薄层层析,从小麦抗寒与不抗寒品系天然橡胶胶乳分离提纯出6种单半乳糖和双半乳糖双甘油酯。并比较了它们的疏水侧链的脂肪酸组成。小麦糖脂疏水侧链脂肪酸的不饱和指数远大于天然胶乳糖脂。抗寒品系胶乳糖脂疏水侧链脂肪酸不饱和指数大于不抗寒品系。双半乳糖双甘油酯疏水侧链脂肪酸不饱和指数均大于其单半乳糖糖脂。 相似文献
46.
Gamma-crystallins of the human eye lens: expression analysis of five members of the gene family. 总被引:6,自引:1,他引:5 下载免费PDF全文
While only two gamma-crystallins have been identified in the human eye lens, molecular studies indicate that the human gamma-crystallins are encoded in a multigene family comprising at least seven closely related members. Sequence analysis of five of these genes has suggested that three (gamma 1-2, G3, and G4) are potentially active, while two (G1 psi and G2 psi) correspond to closely related pseudogenes. Here we report on the detailed structure of a sixth gamma-crystallin gene, G5, and our results obtained with transient expression assays to characterize both the promoter activity and translation products of five members of the gene family. We show that 5'-flanking sequences of G1 psi and G2 psi lacked detectable promoter activity, while the corresponding sequences of G3, G4, and G5 were able to direct high levels of expression of the bacterial chloramphenicol acetyltransferase gene in primary lens epithelia, but not in cultures of nonlens origin. Detailed sequence comparisons indicated that active genes contained several conserved sequence tracts 5' of the TATA box which may constitute functional elements of a lens-specific gamma-crystallin promoter. Expression of the gamma-crystallin coding sequences from the human metallothionein IIA promoter in nonlens cells facilitated characterization of the polypeptides encoded by individual gamma-genes and, in future studies, should permit comparison of these proteins with distinct gamma-crystallins in the human lens. 相似文献
47.
48.
The kinematics of an area-conserving tank-treading disk-shaped red blood cell membrane is studied using the stream function
method suggested by Secomb and Skalak (Q. Jl Mech. appl. Math.
35, Pt 2, 233–247, 1982). Two simple area-conserving velocity fields are superimposed to satisfy the continuity condition at
the curved edges of the disk. A differential equation for the trajectory of any material point of the membrane is derived.
The requirement of synchrony of the cycle for all membrane points leads to an integral equation which determines a magnitude
function. An approximate solution is made possible by assuming small trajectory deflections. 相似文献
49.
50.
Summary The production of 9-cis-1, 18-octadecenedioic acid from different substrates by the mutant S76 of Candida tropicalis was studied. It was found that the mutant could convert oleyl alcohol, oleic acid, and methyl oleate to 9-cis-1, 18-octadecenedioic acid through either the diterminal oxidation of the alcohol or the -oxidation of the terminal methyl group of the mono acid. The geometric configuration of the product was identified by different analytical methods. The results demonstrated that no change in the geometric configuration of molecular structure happened during the bioconversion of such unsaturated substrates to 9-dioic acid. To enhance the production of this dioic acid in the medium, calcium carbonate was added as a trapping agent. The IR spectrum, 1H NMR and 13C-satellite spectra of this compound were presented.Dedicated to Professor Dr. K. Esser on the occasion of his 65th birthday 相似文献