全文获取类型
收费全文 | 53137篇 |
免费 | 17366篇 |
国内免费 | 2315篇 |
出版年
2024年 | 36篇 |
2023年 | 258篇 |
2022年 | 602篇 |
2021年 | 1310篇 |
2020年 | 2748篇 |
2019年 | 4403篇 |
2018年 | 4498篇 |
2017年 | 4697篇 |
2016年 | 4923篇 |
2015年 | 5397篇 |
2014年 | 5297篇 |
2013年 | 5981篇 |
2012年 | 4223篇 |
2011年 | 3623篇 |
2010年 | 4448篇 |
2009年 | 3099篇 |
2008年 | 2377篇 |
2007年 | 1883篇 |
2006年 | 1743篇 |
2005年 | 1697篇 |
2004年 | 1514篇 |
2003年 | 1390篇 |
2002年 | 1266篇 |
2001年 | 949篇 |
2000年 | 839篇 |
1999年 | 700篇 |
1998年 | 343篇 |
1997年 | 246篇 |
1996年 | 234篇 |
1995年 | 232篇 |
1994年 | 195篇 |
1993年 | 149篇 |
1992年 | 215篇 |
1991年 | 174篇 |
1990年 | 152篇 |
1989年 | 153篇 |
1988年 | 107篇 |
1987年 | 111篇 |
1986年 | 100篇 |
1985年 | 79篇 |
1984年 | 49篇 |
1983年 | 62篇 |
1982年 | 30篇 |
1981年 | 35篇 |
1980年 | 20篇 |
1979年 | 36篇 |
1978年 | 29篇 |
1977年 | 26篇 |
1976年 | 19篇 |
1972年 | 20篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
241.
Tubular Transport Maxima of PAH and Diodrast Measured Individually in the Aglomerular Kidney of Lophius, and Simultaneously as Competitors Under Conditions of Equimolar Loading
下载免费PDF全文
![点击此处可从《The Journal of general physiology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
The maximal tubular transfer rates (Tm) of both p-aminohippurate (PAH) and diodrast (3,5-diiodo-4-pyridone-N-acetic acid or iodopyracet) were found to be fixed and reproducible when measured separately in Lophius (goosefish) under standard laboratory conditions. Expressed on a molar basis TmPAH was four times TmD. However, when these transport competitors were presented simultaneously in equimolar concentrations with the plasma levels of each sufficiently high enough to saturate the carrier system, the relative rates of excretion were reversed with the diodrast transfer rate then four times that of PAH. The combined rate of excretion was far below TmPAH alone, and roughly equal to TmD. Interaction with a common carrier was indicated by the gradations in degree of inhibition which resulted when plasma concentration ratios of diodrast to PAH were extended from 0.1 to 3.2, and PAH transfer rates expressed as percentage of TmPAH were correspondingly depressed from 17 to 1.0 per cent respectively. These observations again point up the inverse relationship between transfer rate and competitive effectiveness which exists for members of a series of substances actively transported by a common mechanism. It appears that carrier affinity and dissociation characteristics may be quite different for various compounds in a series, and also that these parameters may vary significantly from species to species. 相似文献
242.
243.
244.
T D Nguyen 《BioTechniques》1989,7(3):238-240
245.
Large-scale mapping and chromosome jumping in the q27 region of the human X chromosome 总被引:2,自引:0,他引:2
We have used pulsed field gel electrophoresis for further physical mapping studies in the q27 region of the human X chromosome. We show that the DXS 102 locus and the F9 gene are separated by only 300 kb despite a genetic distance of 1.4 cM; this linkage orients our large-scale map and shows that the mcf.2 transforming sequence is telomeric to F9. A BssHII complete-digest jumping library was used to jump toward the DXS 105 locus; a 130-kb jump was achieved and the corresponding "linking clone" was obtained. 相似文献
246.
Molecular dissection of the NH2-terminal signal/anchor sequence of rat dipeptidyl peptidase IV 总被引:7,自引:3,他引:4
下载免费PDF全文
![点击此处可从《The Journal of cell biology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Dipeptidyl peptidase IV (DPPIV) is a membrane glycoprotein with a type II orientation in the plasma membrane. As shown in a cell-free translation system, the amino-terminal 34 amino acids of rat DPPIV are involved in translocating nascent polypeptide across the membrane of microsomes and in anchoring the translocated polypeptide in the microsomal membrane. The amino-terminal sequence performing this dual function is composed of: a central hydrophobic core of 22 amino acid residues; 6 amino-terminal residues preceding the hydrophobic core (MKTPWK); and 6 residues following the hydrophobic core. The six residues preceding the hydrophobic core are exposed on the outside (cytoplasmic side) of the microsomal membrane. Site-directed mutagenesis studies show that deletion of this cytoplasmic domain, excluding the amino-terminal initiating methionine, does not affect translocation of nascent DPPIV polypeptide, but does affect significantly anchoring of the translocated polypeptide in the microsomal membrane. In contrast, changing the two cytoplasmic Lys to Glu residues or shortening of the hydrophobic core from 22 to 15 residues or converting the last 11e of the shortened hydrophobic core into Ala affects neither translocation across nor anchoring of the DPPIV polypeptide in the microsomal membrane. These and other structural features of the DPPIV amino-terminal signal-anchor sequences are discussed along with other types of sequences for their role in targeting nascent polypeptides to the RER. 相似文献
247.
K C Wang S Huh S T Hong J Y Chai K S Choi S H Lee 《The Korean journal of parasitology》1990,28(1):1-10
To establish an animal model of intracranial sparganosis, the fate and behavior of the experimentally inoculated spargana were observed. A total of 102 scolices of spargana were injected into 22 cat brains, and the cats were sacrificed at 2 weeks, 1 month, 3 months and 6 months after the inoculation. Neurosparganosis was established in 77% of the cats. Of 43 recovered worms, 19 (44%) were located in the subdural or subarachnoid space, 16 (37%) in the brain parenchyme, and 2 (5%) in the lateral ventricle. One was detected at the diploic space of the skull and 5 were outside the cranial cavity. All but one were alive, and had grown tails. They were distributed in the brain parenchyme randomly. There was no place which they could not invade. No adult was found in the intestine. Cerebrospinal fluid (CSF) was collected before inoculation, 1 week, 2 weeks, 1 month, 3 months and 6 months after inoculation. The level of anti-sparganum IgG antibody in CSF measured by ELISA began to increase above the criteria of positivity 1 month after inoculation. Three months after inoculation, the values markedly increased. The present findings reveal that intracranial inoculation of spargana into the brains of cats would be a good animal model of experimental neurosparganosis. 相似文献
248.
Q C Shen V Simplaceanu P F Cottam J L Wu J S Hong C Ho 《Journal of molecular biology》1989,210(4):859-867
The results of molecular genetic, biochemical and nuclear magnetic resonance studies on glutamine-binding protein of Escherichia coli suggest that the only two tryptophan residues, at positions 32 and 220, in the protein molecule are likely to be involved in (or sensitive to) interactions with the membrane-bound protein components of the glutamine transport system. It has been found that both tryptophan residues have limited motional freedom, are located away from the surface of the protein molecule and are not close to the ligand-binding site. Their presence, however, is required for the optimal transport of L-glutamine across the cytoplasmic membrane, though not essential for the ligand-binding process. The relevance of these results to the structure and function of the glutamine-binding protein in the glutamine transport system is discussed. 相似文献
249.
250.
短尾猴(Macaca arctoides)和猕猴跟骨的功能形态研究 总被引:4,自引:0,他引:4
本文从形态描述和统计入手,对短尾猴(macaca arctoides)和猕猴的跟骨进行了比较研究。结果表明,所研究的跟骨变量无论数值大小还是几何图形结构都存在一定差异。特别是跟骨最大宽、跟长、后距骨连结面长、跟骨高度及相对跟长存在显著性差异水平。猕猴跟骨变量间的相关关系比短尾猴的表现得更为紧密。据其形态与功能的关系,我们认为:与猕猴相较,短尾猴更适应于地栖生活。这似乎与短尾猴具更大的体重有关。 相似文献