全文获取类型
收费全文 | 2360篇 |
免费 | 218篇 |
国内免费 | 4篇 |
出版年
2022年 | 36篇 |
2021年 | 49篇 |
2020年 | 19篇 |
2019年 | 38篇 |
2018年 | 47篇 |
2017年 | 40篇 |
2016年 | 59篇 |
2015年 | 96篇 |
2014年 | 93篇 |
2013年 | 106篇 |
2012年 | 171篇 |
2011年 | 135篇 |
2010年 | 97篇 |
2009年 | 66篇 |
2008年 | 114篇 |
2007年 | 94篇 |
2006年 | 96篇 |
2005年 | 77篇 |
2004年 | 70篇 |
2003年 | 69篇 |
2002年 | 62篇 |
2001年 | 51篇 |
2000年 | 47篇 |
1999年 | 42篇 |
1998年 | 28篇 |
1997年 | 19篇 |
1996年 | 17篇 |
1995年 | 23篇 |
1994年 | 21篇 |
1992年 | 33篇 |
1991年 | 37篇 |
1990年 | 41篇 |
1989年 | 33篇 |
1988年 | 48篇 |
1987年 | 34篇 |
1986年 | 27篇 |
1985年 | 37篇 |
1984年 | 28篇 |
1983年 | 26篇 |
1982年 | 25篇 |
1981年 | 18篇 |
1980年 | 15篇 |
1979年 | 25篇 |
1977年 | 19篇 |
1976年 | 16篇 |
1975年 | 27篇 |
1974年 | 31篇 |
1973年 | 27篇 |
1972年 | 17篇 |
1968年 | 16篇 |
排序方式: 共有2582条查询结果,搜索用时 0 毫秒
991.
The cell suspension of Leishmania donovani incorporates 14CO2 resulting in the formation of [14C]-succinic acid under anaerobic conditions. The results showed that the [14C]-succinate formation from [1-14C]-glucose is much greater than that from [6-14C]-glucose. [14C-pyruvate] takes part in the production of succinic acid under anaerobic conditions without decarboxylation. The anaerobic formation of succinate appears to involve the production of malate, which is then converted to succinate via the reduction of fumarate by the reversal of the tricarboxylic acid cycle. Evidence indicated that the active species in this carboxylation reaction was CO2 although HCO3 was active to some extent. 相似文献
992.
Probir Chatterjee 《Hydrobiologia》1976,49(2):171-174
The paper deals with cytotaxonomic studies of three forms ofChara braunii-f.coromandelina (n = 14), f.schweinitzii (n = 14) and f.kurzii (n = 28) from West Bengal (India). An improved technique involving the use of a pretreating agent permitted a detailed analysis of the karyotypes of the three taxa studied. It has been concluded that structural alterations of chromosomes and polyploidy are associated with evolution of phenotypic differences in theChara braunii complex. The phylogenetic status ofChara braunii in the light of the present investigation is discussed. 相似文献
993.
O-Acetyl groups as a component of the bacteriophage receptor on Staphylococcus aureus cell walls 总被引:6,自引:2,他引:4
下载免费PDF全文
![点击此处可从《Journal of bacteriology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
The capacity of Staphylococcus aureus H cell walls to inactivate bacteriophage 52A was lost by removing O-acetyl groups but not by removing ester-linked d-alanine. 相似文献
994.
A fungus isolated from West Bengal soil was found to accumulate gluconic acid in shake culture conditions in a mineral salt medium and identified asPenicillium janthinellum. The suitability of different carbon and nitrogen sources in liquid medium for gluconic acid production was studied. Glucose (30 %) and ammonium chloride (300 mg N per L) were most suit able carbon and nitrogen sources, respectively. With C and N sources at the optimal level the st rain accumulated 128 g calcium gluconate per litre. 相似文献
995.
The lactate dehydrogenase isozyme system for five Channa species (snakehead fish) have been examined by means of polyacrylamide gel electrophoresis. The pattern and distribution of the LDH isozymes in all these species are found to be species-specific with a reversed relative mobility of the A and B subunits as compared to most of the other vertebrates. In addition to these two subunits, an eye-specific LDH E isozyme has also been detected in these species. 相似文献
996.
997.
S Roy S Chatterjee S L Taneja G L Kumari I S Allag H C Pandey Y N Jadhav 《Indian journal of experimental biology》1977,15(12):1177-1181
The effect of Centchroman, 3,4-trans-2,2-dimethyl-3-phenyl-4-para-(beta -pyrrolidinoethocy)-phenyl-7-methorychroman, administration was investigated in normospermic and oligospermic subjects. 3 normal volunteers, aged 32-40 years, were treated with increasing doses (30, 60, and 120 mg/day, each dose for 2 weeks). The sperm count was decreased in 1 volunteer but the percentages of nonmotile and abnormal spermatozoa were increased in all 3. There was no change in plasma testosterone and urinary 17-ketosteroid (17-KS) levels but the 17-ketogenic steroids (17-KGSs) were decreased in all of them. 3 out of 5 oligospermic subjects, aged 24-35 years, who received 30 mg/day for 6 weeks revealed increased sperm counts. Plasma testosterone levels were decreased in 4, urinary 17-KGSs were decreased in 2, and 17-KSs were decreased in 1 subject. Acid phosphatase, fructose, sialic acid and glycerylphosphoryl choline levels in semen, and serum glutamate oxaloacetate transaminase, serum glutamate pyruvate transaminase, alkaline phosphatase, and urea in blood were not markedly altered in either group. 相似文献
998.
The Caenorhabditis elegans spe-38 gene encodes a novel four-pass integral membrane protein required for sperm function at fertilization 总被引:1,自引:0,他引:1
Chatterjee I Richmond A Putiri E Shakes DC Singson A 《Development (Cambridge, England)》2005,132(12):2795-2808
A mutation in the Caenorhabditis elegans spe-38 gene results in a sperm-specific fertility defect. spe-38 sperm are indistinguishable from wild-type sperm with regards to their morphology, motility and migratory behavior. spe-38 sperm make close contact with oocytes but fail to fertilize them. spe-38 sperm can also stimulate ovulation and engage in sperm competition. The spe-38 gene is predicted to encode a novel four-pass (tetraspan) integral membrane protein. Structurally similar tetraspan molecules have been implicated in processes such as gamete adhesion/fusion in mammals, membrane adhesion/fusion during yeast mating, and the formation/function of tight-junctions in metazoa. In antibody localization experiments, SPE-38 was found to concentrate on the pseudopod of mature sperm, consistent with it playing a direct role in gamete interactions. 相似文献
999.
This year marks the 50th anniversary of the coiled-coil triple helical structure of collagen, first proposed by Ramachandran's group from Madras. The structure is unique among the protein secondary structures in that it requires a very specific tripeptide sequence repeat, with glycine being mandatory at every third position and readily accommodates the imino acids proline/hydroxyproline, at the other two positions. The original structure was postulated to be stabilized by two interchain hydrogen bonds, per tripeptide. Subsequent modeling studies suggested that the triple helix is stabilized by one direct inter chain hydrogen bond as well as water mediated hydrogen bonds. The hydroxyproline residues were also implicated to play an important role in stabilizing the collagen fibres. Several high resolution crystal structures of oligopeptides related to collagen have been determined in the last ten years. Stability of synthetic mimics of collagen has also been extensively studied. These have confirmed the essential correctness of the coiled-coil triple helical structure of collagen, as well as the role of water and hydroxyproline residues, but also indicated additional sequence-dependent features. This review discusses some of these recent results and their implications for collagen fiber formation. 相似文献
1000.
Hudson AO Bless C Macedo P Chatterjee SP Singh BK Gilvarg C Leustek T 《Biochimica et biophysica acta》2005,1721(1-3):27-36
With the aim of elucidating how plants synthesize lysine, extracts prepared from corn, tobacco, Chlamydomonas and soybean were tested and found to lack detectable amounts of N-alpha-acyl-L,L-diaminopimelate deacylase or N-succinyl-alpha-amino-epsilon-ketopimelate-glutamate aminotransaminase, two key enzymes in the central part of the bacterial pathway for lysine biosynthesis. Corn extracts missing two key enzymes still carried out the overall synthesis of lysine when provided with dihydrodipicolinate. An analysis of available plant DNA sequences was performed to test the veracity of the negative biochemical findings. Orthologs of dihydrodipicolinate reductase and diaminopimelate epimerase (enzymes on each side of the central pathway) were readily found in the Arabidopsis thaliana genome. Orthologs of the known enzymes needed to convert tetrahydrodipicolinate to diaminopimelic acid (DAP) were not detected in Arabidopsis or in the plant DNA sequence databases. The biochemical and reinforcing bioinformatics results provide evidence that plants may use a novel variant of the bacterial pathways for lysine biosynthesis. 相似文献