全文获取类型
收费全文 | 14699篇 |
免费 | 1240篇 |
国内免费 | 25篇 |
出版年
2022年 | 104篇 |
2021年 | 213篇 |
2020年 | 140篇 |
2019年 | 169篇 |
2018年 | 258篇 |
2017年 | 223篇 |
2016年 | 305篇 |
2015年 | 425篇 |
2014年 | 547篇 |
2013年 | 856篇 |
2012年 | 809篇 |
2011年 | 777篇 |
2010年 | 466篇 |
2009年 | 448篇 |
2008年 | 646篇 |
2007年 | 690篇 |
2006年 | 628篇 |
2005年 | 655篇 |
2004年 | 605篇 |
2003年 | 573篇 |
2002年 | 575篇 |
2001年 | 442篇 |
2000年 | 480篇 |
1999年 | 439篇 |
1998年 | 173篇 |
1997年 | 147篇 |
1996年 | 136篇 |
1995年 | 158篇 |
1994年 | 140篇 |
1993年 | 145篇 |
1992年 | 344篇 |
1991年 | 245篇 |
1990年 | 261篇 |
1989年 | 257篇 |
1988年 | 363篇 |
1987年 | 221篇 |
1986年 | 184篇 |
1985年 | 173篇 |
1984年 | 133篇 |
1983年 | 128篇 |
1982年 | 89篇 |
1981年 | 96篇 |
1979年 | 107篇 |
1978年 | 91篇 |
1977年 | 63篇 |
1976年 | 65篇 |
1975年 | 64篇 |
1974年 | 89篇 |
1973年 | 67篇 |
1972年 | 63篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
Preferential expression of cellular retinoic acid binding protein in a subpopulation of neural cells in the developing mouse embryo 总被引:2,自引:0,他引:2
Marie-Josée Vaessen Erika Kootwijk Dirk Bootsma Ad Geurts van Kessel Christine Mummery John Hilkens 《Differentiation; research in biological diversity》1989,40(2):99-105
The cellular retinoic acid binding protein is thought to be involved in the retinoic-acid-mediated signal transduction pathway. We have isolated the mouse cellular retinoic acid binding protein cDNA from an embryonal-carcinoma-derived cell line by using differential cDNA cloning strategies. In situ hybridization on sections of mouse embryos of various developmental stages indicated that the cellular retinoic acid binding protein gene, which we localized on mouse chromosome 9, is preferentially expressed in a subpopulation of neurectodermal cells. This restricted expression pattern suggests an important role for cellular retinoic acid binding protein in murine neurogenesis. 相似文献
32.
Mark T Uhlik Amy N Abell Bruce D Cuevas Kazuhiro Nakamura Gary L Johnson 《Biochimie et biologie cellulaire》2004,82(6):658-663
Mitogen-activated protein kinase (MAPK) pathways are activated by a plethora of stimuli. The literature is filled with papers describing the activation of different MAPKs by almost any stimulus or insult imaginable to cells. In this review, we use signal transduction wiring diagrams to illustrate putative upstream regulators for the MAPK kinase kinases, MEKK1, 2, and 3. Targeted gene disruption of MEKK1, 2, or 3 defined phenotypes for each MEKK associated with loss of specific MAPK regulation. Genetic analysis of MEKK function clearly defines specific components of the wiring diagram that require MEKK1, 2, or 3 for physiological responses. We propose that signal transduction network wiring diagrams are valuable tools for hypothesis building and filtering physiologically relevant phenotypic responses from less connected protein relations in the regulation of MAPK pathways. 相似文献
33.
Raymond L. White Jean-Marc Lalouel G. Mark Lathrop Mark F. Leppert Yusuke Nakamura Peter O'Connell 《The Western journal of medicine》1987,147(4):423-427
Although a number of human genes that cause disease have been traced through the defective product, most genetic defects are recognized only by phenotype. When the biochemical defect is unknown, a gene can be located only through molecular approaches based on coinheritance (genetic linkage) of the disease phenotype with a particular allele of a polymorphic DNA marker that has already been mapped to a specific chromosomal region. Linkage studies in affected families have already localized genes for several important diseases, including cystic fibrosis. Finding a genetic linkage in families in which a disease segregates requires that the human genetic map have a large number of polymorphic markers; when the map is dense enough, any disease gene can be located by linkage to a known marker. Many DNA segments with a high degree of polymorphism are being found and mapped as markers in normal reference pedigrees. Genetic linkage mapping has implications even broader than its application to prenatal diagnosis or therapeutic strategy; analyzing mutations in important genes will illuminate basic mechanisms in molecular biology and the early events that lead to cancer and other disorders. 相似文献
34.
K Sakai T Kobayashi T Komuro S Nakamura K Mizuta Y Sakanoue E Hashimoto H Yamamura 《Biochemistry international》1987,14(1):63-70
Phosphorylation of clupeine sulfate by purified rat brain calcium-activated, phospholipid-dependent protein kinase (protein kinase C) was studied. In the absence of Ca2+, phosphatidylserine and diolein markedly stimulated its phosphorylation. However Ca2+ did not stimulate but inhibit this phosphorylation about 30% in the presence of phospholipids. Random polymer (Arg, Ser) 3:1 and (Lys, Ser) 3:1 could be phosphorylated by protein kinase C. In the presence of phospholipids Ca2+ is not needed for the phosphorylation of polymer (Arg, Ser) 3:1, while Ca2+ is necessary for polymer (Lys, Ser) 3:1. Non-requirement of Ca2+ on clupeine phosphorylation by protein kinase C is briefly discussed. 相似文献
35.
36.
Yasumasa Kunifuji Terumasa Nakamura Masayuki Takasugi 《Biological trace element research》1987,14(3):237-248
Cd induced changes of Zn and Cd distribution in the liver and kidneys were studied in relation to Cd metallothionein (MT)
synthesis. Wistar male rats were given CdCl2 by sc injection of .8, 1.5, and 3.0 mg Cd/kg three times a week for three weeks. Cd levels of liver and kidneys increased
with the increment of Cd dosage and 80–90% of Cd was found in the cytosol. The MT fractions contained 80–89% cytosolic Cd
in the liver and 55–75% Cd in the kidneys. Zn concentrations in the liver increased following Cd administration, But Zn in
the kidneys showed only slight increase. There was a distinct decrease of Cu concentration in the liver of the 3.0 mg group.
In contrast, Cu concentrations in the kidneys increased about three times in the .8 and 1.5 mg Cd groups, but Cu in the 3.0
mg group showed only 1.5 times increase. The changes of these metal concentrations were observed mainly in the cytosol. Non-MT-Cd
in the kidneys was maximum in the 1.5 mg group, but the 3.0 mg group showed significant decrease. In parallel with this decrease
of Cd, Cu and Zn in the kidneys showed similar decrease. When the kidneys are injured, Zn and Cu appear to leak from this
organ. 相似文献
37.
Jaroslav Votruba Jarmila Pazlarová Milada Dvořáková Kalju Vanatalu Libuše Váchová Marie Strnadová Helena Kučerová Jiří Chaloupka 《Applied microbiology and biotechnology》1987,26(4):373-377
Summary A mathematical model was formulated to describe the kinetics and stoichiometry of growth and proteinase production in Bacillus megaterium. Synthesis of the extracellular proteinase in a batch culture is repressed by amino acids. The specific rate of formation of the enzyme (r
E) can be described by the formula {ie373-1}, where k
2 and k
3 stand for the non-repressible and repressible part of enzyme synthesis respectively, k
S
2 is a repression coefficient and S
2 indicates the concentration of amono acids; the values of k
2 and k
S
2 depend on the composition of the mixture of amino acids. Even in a high concentration, a single amino acid is less effective than a mixture of amino acids. The dependence of the proteinase repression on the concentration of an external amino acid (leucine) follows the same course as its rate of incorporation into proteins, approaching saturation at concentrations higher than 50 M (half saturation approximately 10 M). However, the total uptake of leucine did not exhibit any saturation even at 500 M external concentration.Symbols
X
biomass concentration, g/l
-
E
proteinase concentration, unit/l
-
t
time, h
-
S
1
concentration of glucose, g/l
-
S
2
concentration of amino acids, g/l
-
specific growth rate, l/h
-
rE
specific rate of enzyme production, unit/g/h
-
k
1
growth kinetic constant, l/h
-
k
2
product formation kinetic constant (for non-repressible part of enzyme synthesis), unit/g
-
k
3
product formation kinetic constant (for repressible portion of enzyme synthesis), unit/g
-
k
S
1
saturation constant, g/l
-
k
S
2
repression coefficient for a certain amino acid or amino acids mixture, g/l 相似文献
38.
Toshiro Akino Nobuyuki Nakamura Koki Horikoshi 《Applied microbiology and biotechnology》1987,26(4):323-327
Summary An alkalophilic bacterium producing high amounts of the cell-associated -mannosidase and extracellular -mannanase was isolated from soil. The isolate (AM-001) that grew well in alkaline pH media was identified as a strain of Bacillus sp. The optimal cultivation temperature for enzyme production was 31° C for -mannosidase and 37° C for -mannanase with the optimum production medium composed of 1% konjac powder, 0.2% yeast extract, 2% Polypepton, 0.1% K2HPO4, 0.02% MgSO4 · 7H2O and 0.5% Na2CO3. Optimum pH and temperature for -mannosidase were 7.0 and 55° C, and for -mannanase were 9.0 and 65° C. 相似文献
39.
N-terminal deletion in the src gene of Rous sarcoma virus results in synthesis of a 45,000-Mr protein with mitogenic activity. 总被引:4,自引:2,他引:2
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)
D Laugier M Marx J V Barnier F Poirier P Genvrin P Dezle G Calothy 《Journal of virology》1987,61(8):2523-2529
Expression of the v-src gene of Rous sarcoma virus in avian embryo neuroretina cells results in transformation and sustained proliferation of these normally resting cells. Transformed neuroretina cells are also tumorigenic upon inoculation into immunodeficient hosts. We have previously described conditional mutants of Rous sarcoma virus encoding p60v-src proteins which induce proliferation of neuroretina cells in the absence of transformation and tumorigenicity. These results suggest that p60v-src is composed of functionally distinct domains which may interact with multiple cellular targets. In this study, we describe a spontaneous variant of Rous sarcoma virus, subgroup E, which carries a deletion of 278 base pairs in the 5' portion of the v-src gene but which has retained the ability to induce proliferation of quail neuroretina cells. The deleted v-src gene encodes a 45,000-molecular-weight phosphoprotein which contains both phosphoserine and phosphotyrosine, is myristylated, and possesses tyrosine kinase activity indistinguishable from that of wild-type p60v-src. Molecular cloning and sequence analysis of the mutant v-src gene have shown that this deletion extends from amino acid 33 to 126 of the wild-type p60v-src. Therefore, this portion of the v-src protein is dispensable for the mitogenic activity of Rous sarcoma virus in neuroretina cells. 相似文献
40.