全文获取类型
收费全文 | 4899篇 |
免费 | 212篇 |
国内免费 | 3篇 |
出版年
2023年 | 8篇 |
2022年 | 26篇 |
2021年 | 53篇 |
2020年 | 27篇 |
2019年 | 55篇 |
2018年 | 79篇 |
2017年 | 51篇 |
2016年 | 95篇 |
2015年 | 130篇 |
2014年 | 177篇 |
2013年 | 326篇 |
2012年 | 331篇 |
2011年 | 294篇 |
2010年 | 200篇 |
2009年 | 198篇 |
2008年 | 331篇 |
2007年 | 298篇 |
2006年 | 319篇 |
2005年 | 300篇 |
2004年 | 321篇 |
2003年 | 294篇 |
2002年 | 280篇 |
2001年 | 57篇 |
2000年 | 61篇 |
1999年 | 53篇 |
1998年 | 67篇 |
1997年 | 49篇 |
1996年 | 43篇 |
1995年 | 41篇 |
1994年 | 33篇 |
1993年 | 40篇 |
1992年 | 50篇 |
1991年 | 47篇 |
1990年 | 45篇 |
1989年 | 49篇 |
1988年 | 32篇 |
1987年 | 15篇 |
1986年 | 26篇 |
1985年 | 30篇 |
1984年 | 29篇 |
1983年 | 27篇 |
1982年 | 22篇 |
1981年 | 13篇 |
1980年 | 16篇 |
1979年 | 13篇 |
1978年 | 7篇 |
1977年 | 9篇 |
1976年 | 8篇 |
1975年 | 16篇 |
1973年 | 6篇 |
排序方式: 共有5114条查询结果,搜索用时 343 毫秒
11.
The effects of several imidazole antimycotic agents, an imidazole and several mineralocorticoid analogs on the cytochrome P-450(11)beta-catalyzed 11 beta-hydroxylation of 11-deoxycorticosterone and aldosterone synthesis were examined. Ketoconazole, clotrimazole, miconazole and etomidate were found to be potent inhibitors of the reactions, causing 50% inhibition of the 11 beta-hydroxylase activity at concentrations between 10(-8) and 10(-7) M. The potency of etomidate as to the inhibition of aldosterone- and 18-hydroxycorticosterone-production was found to be almost equal to that in the case of 11 beta-hydroxylation. Spironolactone and other newly synthesized mineralocorticoid analogs were also found to inhibit the cytochrome P-450(11)beta-mediated reactions. The ID50 values of these drugs for inhibition of the 11 beta-hydroxylase activity were almost equal to those in the case of the aldosterone- and 18-hydroxycorticosterone-biosynthetic activities. The results of kinetical studies indicated that one of the mineralocorticoid analogs, Compound 23-0586, acts as a competitive inhibitor for the cytochrome P-450(11)beta-mediated reactions. 相似文献
12.
The kinetic parameters of ribulose-1,5-bisphosphate (RuBP) carboxylase/oxygenase (EC 4.1.1.39) in wheat (Triticum aestivum L.) and rice (Oryza sativa L.) were determined by rapidly assaying the leaf extracts. The respective K
m and V
max values for carboxylase and oxygenase activities were significantly higher for wheat than for rice. In particular, the differences in the V
max values between the two species were greater. When the net activity of CO2 exchange was calculated at the physiological CO2-O2 concentration from these kinetic parameters, it was 22% greater in wheat than in rice. This difference in the in-vitro RuBP-carboxylase/oxygenase activity between the two species reflected a difference in the CO2-assimilation rate per unit of RuBP-carboxylase protein. However, there was no apparent difference in the CO2-assimilation rate for a given leaf-nitrogen content between the two species. When the RuBP-carboxylase/oxygenase activity was estimated at the intercellular CO2 pressure from the enzyme content and kinetic parameters, these estimated enzyme activities in wheat and rice were similar to each other for the same rate of CO2 assimilation. These results indicate that the difference in the kinetic parameters of RuBP carboxylase between the two species was offset by the differences in RuBP-carboxylase content and conductance for a given leaf-nitrogen content.Abbreviations DTT
dithiothreitol
- EDTA
ethylenediamine-tetraacetic
- PAR
photosynthetically active radiation
- RuBP
ribulose-1,5-bisphosphate 相似文献
13.
Egg yolk lipoprotein promoted growth of a wide variety of mammalian cell lines, including plasma-cytomas and epithelial cell lines, in serum-free medium. The lipoprotein was active for cell growth when used with insulin, transferrin, ethanolamine and selenite. The most active lipoprotein fraction (YLP-pI7.5) was purified to give a single peak by chromatofocusing and gel filtration, and was homogeneous on a 0.35% agarose gel electrophoretogram. The lipoprotein was characterised as a very low density lipoprotein with a protein content of only 1.3%. This lipoprotein had an optimal concentration of 300 g/ml (4 g protein/ml). It was easily separable from proteinous molecules secreted into the serum-free medium by the cells, since it floated on the surface of the medium after addition of ammonium sulfate, to precipitate protein, and centrifugation. An associated structure of lipid and protein seemed to be still necessary for the lipoprotein to exhibit a growth promoting activity. 相似文献
14.
Koji Sode Nobuaki Hori Yoichi Mikami Isao Karube 《Biocatalysis and Biotransformation》1988,2(1):51-57
Asymmetric reduction of 2,6,6,-trimethyl-2-cyclohexene-l,4-dione (4-oxoisophrone) to (6R)-2,2,6-trimethyl-1,4-cyclohexane-dione((3R)-dihydro-4-oxoisophorone) was catalysed by immobilized thermophilic bacteria, Thermomonospora curvata JTS 321. Because of leakage of entrapped cells from gel beads during reactions using culture medium, we optimized the medium to allow the microbial conversion under conditions of controlled cell growth. Of the media screened, liver infusion medium was found to be the most suitable and microbial conversion was achieved without cell leakage from the immobilized gels. Immobilized T. curvata cells were repeatedly used for the asymmetric reduction of 4-oxoisophorone, more than 15 times, with an extent of conversion of 50%. 相似文献
15.
Hiroshi Shinmoto Hiroki Murakami Shun-Ichi Dosako Koji Yamada Hirohisa Omura 《In vitro cellular & developmental biology. Plant》1988,24(6):505-510
Summary Some hybridoma clones made by fusion of a human lymphoblastoid cell line, HO323 with human B lymphocytes, secreted not only
IgA but also IgM-like immunoglobulin molecules. The IgM-like immunoglobulin had a molecular size of 900 K which corresponded
to that of IgM. Immunochemical analyses revealed that the IgM-like immunoglobulin contained two monomeric IgA and three monomeric
IgM molecules. In the IgA moieties, half of original light chains were replaced withx chains derived from the IgM, and vice versa. 相似文献
16.
Chika Kawashima Koji Terayama Masayuki II Shogo Oka Toshisuke Kawasaki 《Glycoconjugate journal》1992,9(6):307-314
The properties of a rat brain glucuronyltransferase, which is presumed to be associated with the biosynthesis of the HNK-1 epitope on sulfoglucuronyl glycolipids, are described. The enzyme required divalent cations for reaction, with maximal activity at 10mm Mn2+, and exhibited a dual optimum at pH 4–5 and pH 6 depending upon the buffer used, with the highest activity at pH 4.5 in MES buffer. This enzyme strictly recognized the Gal1-4GlcNAc terminal structure, and was highly specific for neolacto (type 2) glycolipids as acceptor. The enzyme was localized specifically in the brain, and was barely detected in other issues, including the thymus, spleen, liver, kidney, lung, and sciatic nerve fibres. Phosphatidylinositol and phosphatidylserine increased the enzymatic reaction 4.4- and 2.3-fold, respectively, whereas phosphatidylcholine slightly decreased the rate.Abbreviations GlcA
glucuronic acid
- Lc-PA14
lactotetraose-phenyl-C14H29
- nLc-PA14
neolactotetraose-phenyl-C14H29
- nLcOse4-Cer
neolactotetraosylceramide
- NP-40
Nonidet P-40
- PC
phosphatidylcholine
- PE
phosphatidylethanolamine
- PI
phosphatidylinositol
- PS
phosphatidylserine
- SGGL
sulfoglucuronyl glycolipid 相似文献
17.
Koji Adachi Paul Belser Hans Bender Derui Li Ulrich Rodeck Etty N. Benveniste David Woo Wolff H. Schmiegel Dorothee Herlyn 《Cancer immunology, immunotherapy : CII》1992,34(6):370-376
Summary Recombinant tumor necrosis factor (rTNF; optimal dose 1000 U/ml) significantly increased the density of epidermal growth factor receptor (EGF-R) in three of four glioma cell lines in culture as determined by binding analysis of anti-EGF-R monoclonal antibody (mAb) 425. Since enhancement of EGF-R expression by rTNF- was inhibited when cells were treated with the protein synthesis inhibitor cycloheximide, the effects of rTNF may be protein-synthesis-dependent. The dose of rTNF that was optimal for up-regulation of EGF-R on glioma cells did not inhibit the growth of these cells.125I-labeled mAb 425 lysed glioma cells in culture following its internalization into the cells. After glioma cells had been treated with rTNF, the growth-inhibitory effects of the mAb were significantly enhanced, probably a reflection of the increase in EGF-R density on the tumor cell surfaces. The rTNF effects were specific to the EGF-R and did not affect unrelated glioma-associated antigens. In our previous clinical trials,125I-labeled mAb 425 showed immunotherapeutic effects in glioma patients. The present study provides the basis for considerations of combined immunotherapy of glioma patients with125I-labeled mAb 425 and rTNF. 相似文献
18.
beta 2-Glycoprotein I (beta 2 GPI), a plasma protein that binds to anionic phospholipids, is composed of five repeating units called a short consensus repeat (SCR), which is found mostly in the regulatory proteins of the complement system. Recently the human beta 2 GPI gene has been assigned to chromosome 17, not to chromosome 1 where most of the genes of the SCR-containing proteins are clustered. In this report, we have isolated a full-length cDNA clone of mouse beta 2 GPI and determined the chromosomal localization of the gene. The amino acid sequence deduced from the nucleotide sequence of mouse beta 2 GPI revealed 76.1% identity with that of human beta 2 GPI. A genetic mapping by in situ hybridization and linkage analysis using 50 backcross mice has shown that the mouse beta 2 GPI gene (designated B2gp1) is located on the terminal portion of the D region of chromosome 11, closely linked to Gfap, and is 18 cM distal to Acrb, extending a conserved linkage group between mouse chromosome 11 and human chromosome 17. On the basis of these results, the evolutionary relationships among the SCR-containing proteins are discussed. 相似文献
19.
Phototropic stimulation does not induce unequal distribution of indole-3-acetic acid in maize coleoptiles 总被引:3,自引:0,他引:3
Distribution of endogenous diffusible auxin into agar blocks from phototropically stimulated maize coleoptile tips was studied using a bioassay and a physicochemical assay, to clarify whether phototropism in maize coleoptiles involves a lateral gradient in the amount of auxin. At 50 min after the onset of phototropic stimulation, when the phototropic response was still developing, direct assay of the blocks with the Avena curvature test showed that the auxin activity in the blocks from the shaded half-tips was twice that of the lighted side, at both the first and second positive phototropic curvatures. However, physicochemical determination following purification showed that the amount of indole-3-acetic acid (IAA) was evenly distributed in the blocks from lighted and shaded coleoptile half-tips at both the first and second positive phototropic curvatures. The even distribution of the IAA was also confirmed with the Avena curvature test following purification by HPLC. These results indicate that phototropism in maize coleoptiles is not caused by a lateral gradient of IAA itself and thus cannot be described by the Cholodny-Went theory. Furthermore, the lower auxin activity in the blocks from the lighted half-tips suggests the presence of inhibitor(s) interfering with the action of auxin and their significant diffusion from unilaterally illuminated coleoptile tips. 相似文献
20.
Tomizawa Ken-ichi; Ito Naoko; Komeda Yoshibumi; Uyeda Taro Q. P.; Takio Koji; Furuya Masaki 《Plant & cell physiology》1991,32(1):95-102
The pea phytochrome I (PI) cDNA clone, pPP1001, was expressedin E. coli. The plasmid pPP1001 contains pea PI cDNA which coversthe entire coding region with the Shine-Dalgarno consensus sequencejoined upstream of the cDNA in an expression vector pNUT6. ThepPP1001 transformants formed typical inclusion bodies when culturedat 32?C. However, when cultured at 37?C or in the presence ofisopropyl-ß-D-thiogalactopyranoside (IPTG) at 32?C,the bacteria lysed before inclusion body formation. Immuno-stainingwith anti-PI monoclonal antibody, mAP5, of transformants fixedby cold methanol showed that stainable materials were distributedin whole cytoplasmic region. When the inclusion bodies wereobserved clearly, the regions corresponding to the inclusionbodies became difficult to stain. Western blot analysis, however,showed that a ca. 100 kDa PI polypeptide was detected in thefraction from inclusion bodies and a ca. 90 kDa PI polypeptidefrom the soluble fraction. The amino acid sequence analysisof purified 100 kDa PI sample indicated that its amino terminusis blocked. However, minor signals in one experiment yieldeda sequence corresponding to the expected amino terminus of peaPI except for the initiation methionine. One of the anti-peaPI monoclonal antibodies, mAP9, that recognizes the near N-terminusof pea phytochrome was reactive to the 100 kDa polypeptide. (Received June 22, 1990; Accepted November 18, 1990) 相似文献