全文获取类型
收费全文 | 7262篇 |
免费 | 680篇 |
国内免费 | 696篇 |
出版年
2024年 | 14篇 |
2023年 | 72篇 |
2022年 | 193篇 |
2021年 | 259篇 |
2020年 | 230篇 |
2019年 | 279篇 |
2018年 | 248篇 |
2017年 | 203篇 |
2016年 | 292篇 |
2015年 | 351篇 |
2014年 | 487篇 |
2013年 | 524篇 |
2012年 | 572篇 |
2011年 | 513篇 |
2010年 | 337篇 |
2009年 | 348篇 |
2008年 | 435篇 |
2007年 | 353篇 |
2006年 | 364篇 |
2005年 | 283篇 |
2004年 | 290篇 |
2003年 | 266篇 |
2002年 | 250篇 |
2001年 | 162篇 |
2000年 | 141篇 |
1999年 | 142篇 |
1998年 | 101篇 |
1997年 | 88篇 |
1996年 | 58篇 |
1995年 | 46篇 |
1994年 | 34篇 |
1993年 | 34篇 |
1992年 | 81篇 |
1991年 | 66篇 |
1990年 | 52篇 |
1989年 | 51篇 |
1988年 | 29篇 |
1987年 | 35篇 |
1986年 | 30篇 |
1985年 | 32篇 |
1984年 | 35篇 |
1983年 | 26篇 |
1981年 | 18篇 |
1980年 | 19篇 |
1979年 | 25篇 |
1978年 | 15篇 |
1974年 | 15篇 |
1972年 | 16篇 |
1968年 | 16篇 |
1967年 | 14篇 |
排序方式: 共有8638条查询结果,搜索用时 15 毫秒
11.
Potassium channels from NG108-15 neuroblastoma-glioma hybrid cells. Primary structure and functional expression from cDNAs 总被引:17,自引:0,他引:17
The complete amino acid sequences of two potassium channel proteins from NG108-15 neuroblastoma-glioma hybrid cells have been deduced by cloning and sequencing the cDNAs. One of these proteins (NGK2) is structurally more closely related to the Drosophila Shaw gene product than to the Shaker and Shab gene products, whereas the other (NGK1) is identical with a rat brain potassium channel protein (BK2) which is more closely related to the Drosophila Shaker gene product. mRNAs derived from both the cloned cDNAs, when injected into Xenopus oocytes, direct the formation of functional potassium channels with properties of delayed rectifiers. 相似文献
12.
Cloning of the Membrane-Bound Aldehyde Dehydrogenase Gene of Acetobacter polyoxogenes and Improvement of Acetic Acid Production by Use of the Cloned Gene 总被引:11,自引:2,他引:9
下载免费PDF全文
![点击此处可从《Applied microbiology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Masahiro Fukaya Kenji Tayama Toshimi Tamaki Haruko Tagami Hajime Okumura Yoshiya Kawamura Teruhiko Beppu 《Applied microbiology》1989,55(1):171-176
A genomic clone bank of Acetobacter polyoxogenes NBI1028 constructed in Escherichia coli by use of the expression vector pUC18 was screened with antibody raised against membrane-bound aldehyde dehydrogenase (ALDH; 75 kilodaltons [kDa]) from A. polyoxogenes NBI1028. A clone that synthesized a 41-kDa protein cross-reactive with anti-ALDH antibody was isolated. For cloning of the full-length ALDH structural gene, a cosmid gene bank was screened by Southern blot hybridization with the cloned DNA as a probe, and subcloning from the positive cosmid clone was performed with shuttle vector pMV24. Plasmid pAL25, containing the full-length ALDH structural gene, was isolated and expressed in both E. coli and Acetobacter aceti to produce a fused protein (78 kDa) with a short NH2-terminal β-galactosidase peptide. pAL25 conferred ALDH production on a mutant of A. aceti lacking the enzyme activity. Transformation of A. aceti subsp. xylinum NBI2099 with pAL25 caused 2- and 1.4-fold increases in the production rate and in the maximum concentration of acetic acid in submerged fermentation, respectively. 相似文献
13.
Expression of active alpha-3 subunit of rat brain Na+,K+-ATPase from the messenger RNA injected into Xenopus oocytes 总被引:2,自引:0,他引:2
Y Hara M Ohtsubo T Kojima S Noguchi M Nakao M Kawamura 《Biochemical and biophysical research communications》1989,163(1):102-105
Cloned cDNA encoding the so-far uncharacterized alpha-3 subunit of rat brain Na+,K+-ATPase (Hara et al. (1987) J. Biochem. 102, 43-58, Shull et al. (1986) Biochemistry 25, 8125-8132) was incorporated into a vector carrying the SP6 promoter. The mRNA produced in vitro was injected into Xenopus oocytes with the mRNA encoding the Na+,K+-ATPase beta subunit of Torpedo electroplax. Increased Na+,K+-ATPase activity in the oocyte membrane was observed. This newly expressed activity was inhibited by ouabain (Ki = 1.5 x 10(-7) M), suggesting that the alpha-3 subunit of rat brain Na+,K+-ATPase is a highly ouabain-sensitive catalytic subunit. 相似文献
14.
Manganese-binding proteins of the oxygen-evolving complex 总被引:4,自引:0,他引:4
The extrinsic 33-kDa protein (P33) was cross-linked covalently to the binding site on P33-depleted PSII preparations which is responsible for reconstitution of photosynthetic water oxidation after PSII preparations have been washed with 1 M CaCl2. Conditions were found in which more than half of the cross-linked protein complexes formed in the PSII preparations retained the ability to catalyze the oxidation of water. The complex is composed of the P33 cross-linked to the D1 and D2 proteins and a 34-kDa protein, which is present in lower abundance than the other three proteins. After solubilization of the membranes with SDS and purification by preparative SDS-PAGE, the complex retains bound manganese and can catalyze the conversion of H2O2 to O2. Calcium and chloride increased the catalase activity of the purified cross-linked complex while lanthanum or hydroxylamine abolished the activity. By use of the specific activity of the H2O2-dependent reaction to follow the extent of purification of the cross-linked complex, the most highly purified complex was determined to contain 0.34 microgram of manganese/180 micrograms of protein. The mole ratio of Mn/protein was calculated to range from 3.6 to 4.5 depending on the assumed stoichiometry of the protein subunits. The results presented here provide direct evidence that one or more of the three proteins that have cross-linked to the P33 are responsible for binding the manganese of the oxygen-evolving complex. 相似文献
15.
The lipopolysaccharide of Ectothiorhodospira vacuolata was obtained by the phenol-water procedure. It contained a 3-O-methyl-hexose, glucose, galacturonic and glucuronic acids. The finding of d-glycero-d-mannoheptose and 2-keto-3-deoxyoctonate (tentatively identified) suggested a core-structure. The lipid fraction of the lipopolysaccharide contained phosphate and both, 2,3-diamino-2,3-dideoxy-d-glucose and d-glucosamine. The major fatty acids were amine-bound 3-OH-10:0 and 3-OH-12:0 and esterbound 14:0 and 16:0 Sodium deoxycholate gel-electrophoresis, showing a single band only, indicated R-type character of the lipopolysaccharide of Ectothiorhodospira vacuolata.Abbreviations DOC
sodium deoxycholate
- GC/MS
combined gasliquid chromatography
- PAGE
polyacrylamide gel-electrophoresis 相似文献
16.
Ovulation induced by hCG in rabbits was reduced significantly (P less than 0.005) by sulpiride-induced hyperprolactinaemia. The pre- and post-ovulatory increases in peripheral and ovarian venous progesterone (but not oestradiol or testosterone) were suppressed in the treated animals. The condition of hyperprolactinaemia also prevented the usual changes in 2,4-dinitrophenyl-Pro-Gln-Gly-Ile-Ala-Gly-Gln-D-Arg-OH peptidase (DNP-peptidase) and alpha-N-benzoyl-DL-Arg-beta-naphthylamide hydrolase (BANA-hydrolase) activities in follicular tissue that had been stimulated by an ovulatory dose of hCG. These results suggest that inhibition of progesterone production and collagenolytic enzyme activity by sulpiride-induced hyperprolactinaemia may be responsible for the ovulatory dysfunction that occurs when a mammal has a high level of circulating prolactin. 相似文献
17.
电损毁海马CA3区及连合前穹窿对大鼠血浆胰岛素水平... 总被引:1,自引:0,他引:1
Bilateral electrical lesioning of the hippocampal CA3 region (HCA3-EL) or anterior commissura hippocampi (ACHF-EL) caused marked elevations in plasma basal levels of insulin. 2 weeks later, fasting blood glucose levels were also augmented with decreased glucose tolerance. In contrast, the secretory response of pancreatic B cells to glucose stimulation was markedly enhanced. Following intravenous glucose tolerance test (IVGTT), the relative amounts of glucagon-like and insulin-like immunoreactants were reduced in the pancreatic islets of both HCA3-EL and ACHF-EL rats in comparison with the controls. In the HCA3-EL group, the relative amounts of somatostatin-like immunoreactants and gross numbers of such immunostained cells in islets were also decreased as compared with the control. No difference was seen in pancreatic-polypeptide-like immunoreactivities as assessed by immunohistochemistry plus microphotometry method. The above results suggest strongly that HCA3 and ACHF exert a tonic inhibitory action on the insulin secretion in the rat. 相似文献
18.
活性氧对巨噬细胞呼吸爆发影响及云芝多糖的保护作用 总被引:2,自引:0,他引:2
用化学发光法观察到叔丁基氢过氧化物对培养的小鼠腹腔巨噬细胞呼吸爆发有强烈的抑制作用。云芝多糖经腹腔注射后,能增强巨噬细胞呼吸爆发功能对叔丁基氢过氧化物损伤的抵抗力。云芝多糖处理的巨噬细胞谷胱甘肽过氧化物酶基础活力显著提高,在叔丁基氢过氧化物作用下,云芝多糖处理的巨噬细胞仍有较高的谷胱甘肽过氧化物酶活力。说明巨噬细胞的免疫功能与谷胱甘肽过氧化物酶活力有关,非特异性免疫多糖可提高细胞抗氧化能力,减轻活性氧损伤作用。 相似文献
19.
20.
Michiaki Morohashi Keiko Tsuchiya Takashi Mita Masaru Kawamura 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1991,161(1):69-72
Summary An inhibitory activity to (Na,K)ATPase was found in cell extracts of the brine shrimp, Artemia salina, irrespective of its developmental stages. Organic solvent extraction together with gas chromatographic analysis reveals that the inhibitory activity is due to long-chain, non-esterified fatty acids and their derivatives. Unsaturated fatty acids, especially with cis-configuration, are more effective in inhibition than saturated ones.Abbreviations ATPase
adenosine triphosphatase
- EDTA
ethylenediamine-tetraacetate
- TLC
thin-layer chromatography 相似文献