全文获取类型
收费全文 | 4577篇 |
免费 | 462篇 |
国内免费 | 2篇 |
出版年
2023年 | 21篇 |
2022年 | 67篇 |
2021年 | 130篇 |
2020年 | 71篇 |
2019年 | 95篇 |
2018年 | 98篇 |
2017年 | 100篇 |
2016年 | 166篇 |
2015年 | 219篇 |
2014年 | 275篇 |
2013年 | 299篇 |
2012年 | 387篇 |
2011年 | 370篇 |
2010年 | 233篇 |
2009年 | 190篇 |
2008年 | 280篇 |
2007年 | 269篇 |
2006年 | 235篇 |
2005年 | 220篇 |
2004年 | 178篇 |
2003年 | 161篇 |
2002年 | 159篇 |
2001年 | 43篇 |
2000年 | 27篇 |
1999年 | 33篇 |
1998年 | 33篇 |
1997年 | 21篇 |
1996年 | 23篇 |
1994年 | 18篇 |
1993年 | 26篇 |
1992年 | 26篇 |
1991年 | 25篇 |
1990年 | 19篇 |
1989年 | 24篇 |
1988年 | 24篇 |
1987年 | 22篇 |
1986年 | 23篇 |
1985年 | 29篇 |
1984年 | 26篇 |
1983年 | 20篇 |
1982年 | 23篇 |
1981年 | 20篇 |
1980年 | 18篇 |
1979年 | 19篇 |
1978年 | 20篇 |
1977年 | 15篇 |
1976年 | 19篇 |
1974年 | 26篇 |
1973年 | 19篇 |
1972年 | 16篇 |
排序方式: 共有5041条查询结果,搜索用时 15 毫秒
41.
L Marcus H Ris H O Halvorson R K Bretthauer R M Bock 《The Journal of cell biology》1967,34(2):505-512
This report details the procedural requirements for preparing cell-free extracts of yeast rich in polyribosomes. This enabled us to demonstrate the occurrence of polyribosomes in yeast, to show their role in protein synthesis, and to devise methods for their resolution and isolation. When certain precautions are met (the use of log phase cells, rapidly halting cell growth, gentle methods of disruption, sedimentation through exponential density gradients, etc.), individual polyribosome size classes ranging up to the heptosome can be fractionated and separated from their nearest neighbors. Larger size classes are resolved partially among themselves, free of smaller polyribosomes. This was confirmed by extensive electron micrographic studies of material from the various fractions obtained upon density gradient centrifugation of yeast extracts. Modifications of the gradients and procedure should allow fractionation and isolation of the larger polyribosomes, including those containing polycistronic messages. Yeast polyribosomes are disaggregated to single ribosomes by longer term grinding, cell disruption by the French pressure cell, the Hughes press, or by incubation with dilute RNAse. Yeast polyribosomes are active in the incorporation of amino acids into polypeptide; the single ribosomes exhibit only slight activity. The latter activity is probably due to the presence of a small fraction of monosomes still containing mRNA. Poly-U stimulates amino acid incorporation only in the single ribosomes. 相似文献
42.
Genetic Analysis of Glutamate Transport and Glutamate Decarboxylase in Escherichia coli 总被引:13,自引:10,他引:3
下载免费PDF全文
![点击此处可从《Journal of bacteriology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
The location of the Escherichia coli K-12 genes determining or regulating glutamate transport, and the location of the gene determining glutamate decarboxylase synthesis, were established by conjugation. The ability to grow on glutamate as the sole source of carbon and energy was used to select for glutamate transport recombinants. Two genes determining the ability to grow on glutamate as the sole source of carbon and energy were mapped. One (gltC) is located near mtl (mannitol), and the other (gltH) appears to be located between the gal (galactose) and trp (tryptophan) loci. The glutamate decarboxylase gene (gad) is strongly linked to gltC. The gltC(+) recombinants grow on glutamate much faster and accumulate this amino acid to a greater extent than do the gltH(+) recombinants. The gltH(+) gene functioned only in one female strain (P678), whereas the gltC gene functioned in all the female strains tested (P678, C600, W1). 相似文献
43.
44.
Characterization of two soybean repetitive proline-rich proteins and a cognate cDNA from germinated axes 总被引:18,自引:7,他引:11
下载免费PDF全文
![点击此处可从《The Plant cell》网站下载免费的PDF全文](/ch/ext_images/free.gif)
We have resolved and analyzed two proline-rich proteins isolated from the walls of soybean cells in culture. The proteins are similar in amino acid content, containing 20% proline, 20% hydroxyproline, 20% lysine, 16% valine, 10% tyrosine, and 10% glutamate. The proteins undergo a rearrangement or a limited cleavage in dilute NaOH, but are otherwise remarkably stable to a high concentration of alkali. We have cloned and sequenced a cDNA from soybean axes germinated for 31 hours (1A10-2) coding for a protein that closely corresponds in its amino acid content to that of the proline-rich proteins. The cDNA sequence predicts a decameric repeat of Pro-Pro-Val-Tyr-Lys-Pro-Pro-Val-Glu-Lys. Consequently, this class of proteins is referred to as repetitive proline-rich proteins, i.e., RPRP2 and RPRP3. We have also analyzed RNA gel blots with probes that discriminate between the new cDNA clone and a related cDNA previously reported [SbPRP1; Hong, Nagao, and Key (1987). J. Biol. Chem. 262, 8367-8376]. Messenger RNAs from young seedlings and from soybean suspension cultures correspond primarily to the new RPRP clone (1A10-2), whereas the predominant mRNA accumulating later in the roots corresponds to SbPRP1. 相似文献
45.
Marcus P. Lincoln Smith 《Environmental Biology of Fishes》1989,26(1):29-37
Synopsis A number of factors can influence the accuracy and precision of underwater visual transect techniques. Among these are observer swimming speed and, during multispecies surveys, the effect of counting all fishes on estimates of particular species. This paper examines the effect of these factors on population estimates of inconspicuous fishes (defined as Type 1) in a temperate reef fish assemblage near Sydney, Australia. Counting Type 1 fishes with all others yielded significantly lower estimates of species richness and abundance than when counted alone. This suggests that multispecies surveys should be split into 2 or more counts, using a census procedure that is appropriate to the group of species cencused. Further, the effect of counting all other fishes on estimates of Type 1 fishes varied according to the relative abundance of the former: their effect was lowest when abundance of other fishes was lowest. There was a negative relationship between observer speed and estimated abundance for Type 1 fishes. Survey precision of Type 1 fishes was generally improved by surveying at slower observer speeds. 相似文献
46.
Riva C. Marcus Nicholas W. Gale Mary E. Morrison Carol A. Mason George D. Yancopoulos 《Developmental biology》1996,180(2):786
The Eph family of receptor tyrosine kinases and their ligands can be divided into two specificity subclasses: the Eck-related receptors and their GPI-anchored ligands, and the Elk-related receptors and their transmembrane ligands. Previous reports demonstrated that Eck- and Elk-related receptors in the retina distribute in high temporal–low nasal and high ventral–low dorsal gradients, respectively. While others have focused on complementary ligand gradients in the retinal axon target, the tectum, we report that ligands from each subclass also distribute in gradients opposing those of their corresponding receptors within the retina itself. Moreover, ligand gradients in the retina precede ganglion cell genesis. These results support an intraretinal role for Eph family members in addition to their previously proposed role in the development of retinotectal topography. The distinct distributions of Eph family members suggest that each subclass specifies positional information along independent retinal axes. 相似文献
47.
Actions of Rho family small G proteins and p21-activated protein kinases on mitogen-activated protein kinase family members. 总被引:22,自引:7,他引:15
下载免费PDF全文
![点击此处可从《Molecular and cellular biology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
The mitogen-activated protein (MAP) kinases are a family of serine/threonine kinases that are regulated by distinct extracellular stimuli. The currently known members include extracellular signal-regulated protein kinase 1 (ERK1), ERK2, the c-Jun N-terminal kinase/stress-activated protein kinases (JNK/SAPKs), and p38 MAP kinases. We find that overexpression of the Ste20-related enzymes p21-activated kinase 1 (PAK1) and PAK2 in 293 cells is sufficient to activate JNK/SAPK and to a lesser extent p38 MAP kinase but not ERK2. Rat MAP/ERK kinase kinase 1 can stimulate the activity of each of these MAP kinases. Although neither activated Rac nor the PAKs stimulate ERK2 activity, overexpression of either dominant negative Rac2 or the N-terminal regulatory domain of PAK1 inhibits Ras-mediated activation of ERK2, suggesting a permissive role for Rac in the control of the ERK pathway. Furthermore, constitutively active Rac2, Cdc42hs, and RhoA synergize with an activated form of Raf to increase ERK2 activity. These findings reveal a previously unrecognized connection between Rho family small G proteins and the ERK pathway. 相似文献
48.
Concerted action of RAS and G proteins in the sexual response pathways of Schizosaccharomyces pombe. 总被引:9,自引:4,他引:5
下载免费PDF全文
![点击此处可从《Molecular and cellular biology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
We have shown that the expression of mam2, the gene encoding the Schizosaccharomyces pombe P-factor pheromone receptor, is dependent upon components of the pheromone signal transduction pathway, including Ras1, Gpa1, Byr1 and Byr2, each of which is required for both conjugation and sporulation. Studies of the expression of mam2 in mutant S. pombe cells confirm previous conclusions, based on the ability of cells to sporulate, that the Byr1 protein kinase acts downstream of the Byr2 protein kinase and that both act downstream of Ras1, the S. pombe RAS homolog, and Gpa1, the G alpha component that mediates the occupancy of the mam2 receptor. In addition, our present studies show that Ras1 and Gpa1 each act downstream from the other and hence act in concert. The Spk1 kinase, which is required for conjugation and sporulation and which is a structural and functional homolog of the vertebrate MAP kinases, is not required for mam2 expression. 相似文献
49.
The uptake of lead by two contrasting plant species, radish and red fescue, grown in soils contaminated by mine spoil was investigated. Uptake was found to be poorly correlated either with pH or total Pb concentration in the soils. By contrast, a good correlation was obtained, particularly for red fescue, between Pb uptake and Pb concentration in the solution of equilibrated soil suspensions over a wide range of soil pH, total soil Pb and soil solution Pb concentration.Calculations suggested a similar order of magnitude in the total amounts of Pb taken up by the plants and Pb in the soil solution of the root zone, justifying the latter as a good index of Pb-availability. ei]Section editor: A C Borstlap 相似文献
50.