全文获取类型
收费全文 | 8098篇 |
免费 | 748篇 |
国内免费 | 2篇 |
出版年
2021年 | 90篇 |
2020年 | 64篇 |
2019年 | 67篇 |
2018年 | 80篇 |
2017年 | 85篇 |
2016年 | 135篇 |
2015年 | 255篇 |
2014年 | 251篇 |
2013年 | 304篇 |
2012年 | 447篇 |
2011年 | 380篇 |
2010年 | 241篇 |
2009年 | 230篇 |
2008年 | 323篇 |
2007年 | 347篇 |
2006年 | 300篇 |
2005年 | 277篇 |
2004年 | 262篇 |
2003年 | 287篇 |
2002年 | 253篇 |
2001年 | 239篇 |
2000年 | 203篇 |
1999年 | 211篇 |
1998年 | 96篇 |
1997年 | 77篇 |
1996年 | 88篇 |
1995年 | 85篇 |
1994年 | 72篇 |
1993年 | 79篇 |
1992年 | 157篇 |
1991年 | 157篇 |
1990年 | 125篇 |
1989年 | 133篇 |
1988年 | 139篇 |
1987年 | 108篇 |
1986年 | 97篇 |
1985年 | 104篇 |
1984年 | 99篇 |
1983年 | 81篇 |
1982年 | 60篇 |
1981年 | 56篇 |
1979年 | 83篇 |
1978年 | 67篇 |
1977年 | 68篇 |
1976年 | 54篇 |
1975年 | 46篇 |
1974年 | 87篇 |
1973年 | 51篇 |
1972年 | 58篇 |
1970年 | 61篇 |
排序方式: 共有8848条查询结果,搜索用时 31 毫秒
251.
Summary Seedlings of two mangrove species, Avicennia marina and Aegiceras corniculatum, were grown in a range of salinities and humidities in controlled environment chambers, and Phaseolus vulgaris plants were grown in the glasshouse. The fractionation of carbon isotopes in the three species was correlated with the ratio of intercellular and ambient partial pressures of CO2. The results are consistent with fractionation being due both to diffusion in air and to carboxylation in the leaf. It was concluded that the latter process discriminates against 13CO2 relative to 12CO2 by about 27. 相似文献
252.
The role of de novo synthesis in the regulation of adenosine 5-phosphosulfate sulfotransferase activity by H2S inLemna minor L. was investigate using density labeling with15N applied as15NO
3
–
in the culture medium. While adenosine 5-phosphosulfate sulfotransferase activity was rapidly reduced by H2S and rapidly recovered upon removal of H2S, O-acetyl-L-serine sulfhydrylase (EC 4.2.99.8) did not show changes in extractable activity in response to H2S and could therefore be used as an internal marker enzyme for density labeling. The incorporation of15N into adenosine 5-phosphosulfate sulfotransferase was strongly reduced upon transfer of plants into a H2S-containing atmosphere. Half-maximal labeling was reached only after 70–80 h compared to 40–50 h in the control. After removal of H2S, adenosine 5-phosphosulfate sulfotransferase activity increased to the initial level within 20 h, and the enzyme reached halfmaximal labeling after only 15 h. The time course of the density increase of O-acetyl-L-serine sulfhydrylase was not affected very significantly by H2S. These results provide evidence that de novo synthesis of enzyme protein is involved in the regulation of adenosine 5-phosphosulfate sulfotransferase activity by H2S.Abbreviations APS
adenosine 5-phosphosulfate
- APSSTase
adenosine 5-phosphosulfate sulfotransferase
- BSA
Bovine serum albumine
- DTE
dithioerythritol
- OAS
O-acetyl-L-serine
- OASSase
O-acetyl-L-serine sulfhydrylase
- POPOP
1,4-bis-(5-phenyl-2-oxazolyl)-benzene
- PPO
2,5-diphenyloxazole
This is no. 9 in the series Regulation of Sulfate Assimilation in Plants 相似文献
253.
Richard D. Olson Abba J. Kastin Thomas K. von Almen David H. Coy Gayle A. Olson 《Peptides》1980,1(4):383-385
Twenty-four male albino rats were given daily intraperitoneal injections of vasoactive intestinal polypeptide (VIP), motilin, human gastrin I (1–17) or the diluent control vehicle at a dose of 100 μg/kg for four consecutive days and food intake, water intake, body weight, and running wheel activity were determined every 24 hours. Animals injected with motilin or human gastrin I (1–17) exhibited decreased food intake relative to those injected with VIP or diluent, which did not differ from each other, although food intake increased reliably over days. The mean water consumption followed the same pattern as that of food intake. As expected from the above results, VIP produced weight gains as compared with rats injected with motilin or gastrin but not reliably more than after diluent. A reliable effect of trials for weight gain was the greatest on day three. Running wheel activity was not affected by injections of human gastrin I (1–17), motilin, or diluent but was reliably decreased by VIP. No significant differences existed across days. Although the results indicate that GI peptides may affect behavior when injected systemically and that like other peptides they have multiple effects, caution is urged in the interpretation of behavioral results at this time. 相似文献
254.
Regulation of heparan sulphate metabolism by adenosine 3′:5′-cyclic monophosphate in hepatocytes in culture
下载免费PDF全文
![点击此处可从《The Biochemical journal》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Freshly isolated rat hepatocytes maintained as monolayers in a serum-free medium synthesize sulphated glycosaminoglycans, most of which behave as heparan sulphate and are mainly distributed into intracellular compartments. Cyclic AMP, dibutyryl cyclic AMP, glucagon, noradrenaline, prostaglandin E(1), and theophylline, all drugs and hormones known to increase intracellular cyclic AMP concentrations, decreased the incorporation of (35)SO(4) (2-) into heparan sulphate of intra-, extra- and peri-cellular pools. The inhibition mediated by dibutyryl cyclic AMP was dose-dependent and observed as early as 2h after exposure to the drug. In the presence of 1mm-dibutyryl cyclic AMP, incorporation of (35)SO(4) (2-) or [(14)C]glucosamine into heparan sulphate was decreased to 40-50%, suggesting that dibutyryl cyclic AMP interfered with the synthesis of heparan sulphate. This was further supported by pulse-chase experiments, where dibutyryl cyclic AMP had no effect on the degradation of sulphated glycosaminoglycans. Heparan sulphates synthesized and secreted into the extracellular pool in the presence of dibutyryl cyclic AMP were smaller in size, whereas the degree of sulphation and molecular size of the heparan sulphate chains released by beta-elimination from these proteoglycans were not different from control values. In the presence of 1mm-cycloheximide, (35)SO(4) (2-) incorporation was decreased to 5%. Addition of p-nitrophenyl beta-d-xyloside, an artificial acceptor of glycosaminoglycan chain synthesis, enhanced this incorporation to 18%. Dibutyryl cyclic AMP did not have any inhibitory effect on the synthesis of chains initiated on p-nitrophenyl beta-d-xylosides. Incorporation of [(3)H]serine into heparan sulphate was not affected by dibutyryl cyclic AMP, whereas the degree of substitution of serine residues with heparan sulphate chains was less in heparan sulphate synthesized in the presence of dibutyryl cyclic AMP, suggesting that cyclic AMP exerts its effect on the metabolism of sulphated glycosaminoglycans by affecting the transfer of xylose on to the protein core. 相似文献
255.
V L von Riesen 《Applied microbiology》1980,39(1):92-96
Pseudomonas maltophilia and Pseudomonas putida were identified as alginolytic species. Two media used for demonstrating alginolytic activity are described. The applied aspects of the ability of these two species to digest algin are discussed. 相似文献
256.
W H?rtel J W Betz G von Sengbusch P Bader 《The journal of histochemistry and cytochemistry》1979,27(1):311-314
As a method for the preselection of alarms in gynecological cell samples, the Battelle Cytophotometry Research Group uses the slit-scan technique to obtain various cell parameters, such as the N/C ratio and the relative DNA content, from fluorescently stained cells, which are aligned one-dimensionally in the tape system designed at Battelle. The system developed at Battelle Institute analyzes all signals that exceed the background noise. As the first step in processing the slit-scan data, several threshold levels permit the separation of various artifacts. In subsequent steps, the nuclear peak is recognized, the nuclear boundaries are calculated, and seven cell parameters are determined. For the alarm detection at present only one parameter, DNA fluorescence, is used for these determinations. Visual assignment of these data to definite objects on the tape makes it possible to obtain frequency distributions of: (a) all recorded objects within the sample on the tape; (b) all signals that are classified as cells; and (c) all types of objects that preferentially cause alarms. 相似文献
257.
Summary Specialized transducing phages tna (tryptophanase) harboring chromosomal DNA and genetic markers from the dnaA region of the Escherichia coli chromosome were isolated. Transductional analysis showed that some of these tnaA transducing phages carry two genes important in DNA replication, namely the dnaA gene (initiation of chromosome replication) and the gyrB gene (subunit B of DNA gyrase), formerly designated cou
R. The following clockwise order of genetic markers was found:
uhp, gyrB, dnaA, rimA, tnaA, bglB.The gene-protein relationship was established by the determination of the gene products encoded on the chromosomal DNA of the different tna. A 54 kD and a 91 kD polypeptide appear to be coded for by the dnaA and gyrB genes, respectively; the 91 kD protein is encoded on a region in which coumermycin sensitivity maps and is with respect to electrophoretic behavior identical to subunit B of DNA gyrase. The 54 kD protein is encoded on the region in which different independently isolated dnaA(Ts) mutations (dnaA5, dnaA46, dnaA167, dnaA203, dnaA204, dnaA205, dnaA211, dnaA508) are located. Additional genes which code for polypeptides with hitherto unknown functions were identified and mapped. The acriflavin sensitivity mutation acrB1 was found to be an allele of the gyrB gene (see Note Added in Proof). 相似文献
258.
R E Brouns M Poot R de Vrind T von Hoek-Kon P T Henderson C M Kuyper 《Mutation research》1979,64(6):425-432
When suspensions of freshly isolated rat hepatocytes were exposed to a number of carcinogenic compounds, it was possible to measure an increased UDS by a rapid procedure via liquid-scintillation counting. For a number of carcinogenic compounds and some of their non-carcinogenic structural analogues a good correlation between the carcinogenic property and the ability to induce UDS was demonstrable. Out of 12 carcinogenic compounds, belonging to several different chemical classes, 10 gave rise to an increased UDS, whereas only 2 compounds, the polycyclic aromatic hydrocarbons benzo[alpha]pyrene and benz[alpha]anthracene, did not. All 4 noncarcinogenic compounds tested were negative. Possibly this method can be of value as a routine screening test, in combination with other short-term test systems, thus improving the predictive value of screening in vitro with respect to carcinogenicity. 相似文献
259.
Sprout inhibition of onion bulbs can be effectively accomplished by low doses of radiation [2,3]. However, wholesomeness data on irradiated onions, particularly with respect to their mutagenic activity, are still insufficient for evaluation [6]. Therefore we examined the mutagenic activity of irradiated onions in bacterial systems. Because onion bulbs contain a considerable amount of free amino acids, we used indicator strains carrying the marker for mutagenicity other than the amino acid requirement.In this paper we describe the results on irradiated onions. We used tests with solid and liquid media, assaying for the streptomycin (SM) dependence in a strain having a tetracycline (TC)-resistance factor, as well as DNA repair tests using two sets of indicator strains. 相似文献
260.