全文获取类型
收费全文 | 2211篇 |
免费 | 216篇 |
出版年
2021年 | 43篇 |
2020年 | 25篇 |
2019年 | 37篇 |
2018年 | 29篇 |
2017年 | 28篇 |
2016年 | 62篇 |
2015年 | 84篇 |
2014年 | 82篇 |
2013年 | 134篇 |
2012年 | 120篇 |
2011年 | 155篇 |
2010年 | 83篇 |
2009年 | 67篇 |
2008年 | 93篇 |
2007年 | 94篇 |
2006年 | 91篇 |
2005年 | 105篇 |
2004年 | 99篇 |
2003年 | 57篇 |
2002年 | 75篇 |
2001年 | 28篇 |
2000年 | 52篇 |
1999年 | 26篇 |
1997年 | 21篇 |
1996年 | 16篇 |
1994年 | 19篇 |
1992年 | 33篇 |
1991年 | 33篇 |
1990年 | 33篇 |
1989年 | 26篇 |
1988年 | 33篇 |
1987年 | 29篇 |
1986年 | 24篇 |
1985年 | 30篇 |
1984年 | 23篇 |
1983年 | 20篇 |
1982年 | 26篇 |
1981年 | 24篇 |
1980年 | 18篇 |
1979年 | 23篇 |
1978年 | 17篇 |
1977年 | 23篇 |
1976年 | 28篇 |
1975年 | 24篇 |
1974年 | 23篇 |
1973年 | 18篇 |
1972年 | 18篇 |
1971年 | 20篇 |
1970年 | 16篇 |
1969年 | 16篇 |
排序方式: 共有2427条查询结果,搜索用时 15 毫秒
1.
2.
3.
Richard E. Kouri Raymond Kiefer Eugene M. Zimmerman 《In vitro cellular & developmental biology. Plant》1974,10(1-2):18-25
Summary Two methods for determining the hydrocarbon-metabolizing enzyme activity of cultured mammalian cells were compared. The method
designed to measure benzo[a]an-thracene-induced aryl hydrocarbon hydroxylase activity could detect and quantify enzyme activities
in low passage rodent cells, but could not reproducibly detect levels in intermediate or high passage mouse, rat, or human
cells. The method designed to measure the ability of a cell to convert benzo[a]pyrene from an organic-soluble to an aqueous
acetone-soluble form proved to be more reproducible. This technique, when modified, was demonstrated to be an effective screening
test for the detection of those lines with higher levels of hydrocarbon-metabolizing enzymes.
Supported by the Council for Tobacco Research and Contract NIH 70-2068 within the Virus Cancer Program, National Cancer Institute,
National Institutes of Health. 相似文献
4.
5.
6.
7.
Ribosomes, the universal cellular machines, possess spectacular architecture accompanied by inherent mobility, allowing for their smooth performance as polymerases that translate the genetic code into proteins. The site for peptide bond formation is located within a universal internal semi-symmetrical region, which was identified within all contemporary ribosomes. The high conservation of this region implies its existence irrespective of environmental conditions and indicates that it may represent an ancient RNA molecular apparatus. Hence, we named it the “proto-ribosome”. This prebiotic pocket-like RNA entity is suggested to be capable to accommodate substrates whose stereochemistry enables the creation of chemical bonds. It could have evolved from an earlier catalytic RNA entity that we named the “pre-proto-ribosome”, presumed to be a molecular machine capable of performing various essential tasks in the RNA world, which was snatched by the amino acid invaders for producing proteins. 相似文献
8.
Francesca Fasolo Richard H. Zimmerman Ingrid Fordham 《Plant Cell, Tissue and Organ Culture》1989,16(2):75-87
Leaves taken from micropropagated shoots of several apple (Malus domestica Borkh.) cultivars were cultured in vitro on Linsmaier & Skoog (LS) medium or the rice anther culture medium of Chu et al. (N6) containing various concentrations of either benzyladenine (BA) or thidiazuron (TDZ) plus naphthaleneacetic acid (NAA). Of the TDZ concentrations tested, 10 M was most effective and it was equivalent to, or better than, 22 M BA for both the percentage of leaves regenerating shoots and number of shoots formed per regenerating leaf in almost every experiment. Lower concentrations of NAA (1.1 and 5.4 M) gave best results with both BA and TDZ. N6 medium gave consistently better results than LS. Lowering total salt concentration or total N concentration of LS to that of N6 did not improve the response nor did changing the NO3:NH4 ratio. The 3–4 leaves on the most distal part of the shoot were most responsive and tended to form the most adventitious shoots. Placing the leaf cultures in the dark for the first 2–3 weeks of the culture period produced the best results. Optimum results were obtained by culturing leaves from the distal part of the shoot in the dark for 2 weeks on N6 medium containing 10 M TDZ and 1.1 or 5.4 M NAA, then moving the cultures to 16 h daylight at a photon flux of 60 mol s-1m-2. 相似文献
9.
Kinetic parameters of the protein tyrosine kinase activity of EGF-receptor mutants with individually altered autophosphorylation sites. 总被引:27,自引:4,他引:23 下载免费PDF全文
A Honegger T J Dull D Szapary A Komoriya R Kris A Ullrich J Schlessinger 《The EMBO journal》1988,7(10):3053-3060
Epidermal growth factor (EGF)-receptor mutants in which individual autophosphorylation sites (Tyr1068, Tyr1148 or Tyr1173) have been replaced by phenylalanine residues were expressed in NIH-3T3 cells lacking endogenous EGF-receptors. Kinetic parameters of the kinase of wild-type and mutant receptors were compared. Both wild-type and mutant EGF-receptors had a Km(ATP) 1-3 microM for the autophosphorylation reaction, and a Km(ATP) of 3-7 microM for the phosphorylation of a peptide substrate. These are similar to the Km(ATP) values reported for EGF-receptor of A431 cells. A synthetic peptide representing the major in vitro autophosphorylation site Tyr1173 of the EGF-receptor (KGSTAENAEYLRV) was phosphorylated by wild-type receptor with a Km of 110-130 microM, and the peptide inhibited autophosphorylation with a Ki of 150 microM. Mutant EGF-receptors phosphorylated the peptide substrate with a Km of 70-100 microM. A similar decrease of Km (substrate) was obtained when the phosphorylation experiments were performed with the commonly applied substrates angiotensin II and a peptide derived from c-src. The Km of angiotensin II phosphorylation was reduced from 1100 microM for wild-type receptor to 890 microM for mutant receptor and for c-src peptide from 1010 microM to 770 microM respectively. The Vmax of the kinase was dependent on receptor concentration, but was not significantly affected by the mutation. Analogs of the Tyr1173 peptide in which the tyrosine residue was replaced by either a phenylalanine or an alanine residue also inhibited autophosphorylation with Ki of 650-750 microM. These analyses show that alterations of individual autophosphorylation sites do not have a major effect on kinase activity.(ABSTRACT TRUNCATED AT 250 WORDS) 相似文献
10.