全文获取类型
收费全文 | 5647篇 |
免费 | 343篇 |
国内免费 | 5篇 |
出版年
2023年 | 34篇 |
2022年 | 58篇 |
2021年 | 124篇 |
2020年 | 75篇 |
2019年 | 91篇 |
2018年 | 138篇 |
2017年 | 121篇 |
2016年 | 156篇 |
2015年 | 221篇 |
2014年 | 235篇 |
2013年 | 384篇 |
2012年 | 373篇 |
2011年 | 364篇 |
2010年 | 245篇 |
2009年 | 205篇 |
2008年 | 285篇 |
2007年 | 301篇 |
2006年 | 254篇 |
2005年 | 252篇 |
2004年 | 202篇 |
2003年 | 191篇 |
2002年 | 180篇 |
2001年 | 110篇 |
2000年 | 93篇 |
1999年 | 86篇 |
1998年 | 53篇 |
1997年 | 37篇 |
1996年 | 39篇 |
1995年 | 44篇 |
1994年 | 30篇 |
1993年 | 27篇 |
1992年 | 58篇 |
1991年 | 56篇 |
1990年 | 58篇 |
1989年 | 61篇 |
1988年 | 59篇 |
1987年 | 42篇 |
1986年 | 50篇 |
1985年 | 48篇 |
1984年 | 49篇 |
1983年 | 38篇 |
1982年 | 37篇 |
1981年 | 28篇 |
1980年 | 32篇 |
1979年 | 47篇 |
1978年 | 41篇 |
1977年 | 25篇 |
1976年 | 28篇 |
1975年 | 37篇 |
1974年 | 28篇 |
排序方式: 共有5995条查询结果,搜索用时 281 毫秒
31.
32.
Purification of xylanase, beta-glucosidase, endocellulase, and exocellulase from a thermophilic fungus, Thermoascus aurantiacus 总被引:1,自引:0,他引:1
A strain of thermophilic fungus, Thermoascus aurantiacus, was isolated from local soil. From the culture filtrates of the organism grown on blotting paper, a xylanase, beta-glucosidase, exocellulase, and endocellulase were obtained in large amounts in highly purified form by employing ion-exchange and gel-permeation chromatography. The xylanase was crystallized. The xylanase and endocellulase were stable at 70 degrees C for 8 h, whereas the beta-glucosidase and exocellulase were less stable at 70 degrees C. 相似文献
33.
D S Murthy S K Murthy J K Patel A A Tyagi 《Indian journal of experimental biology》1989,27(10):864-867
An unusual nucleolar organizer region (double NOR) on chromosome 13 was observed in a Down syndrome child [47, XY, +21, dNOR(13)]. The variant chromosome was inherited from the mother [46, XX, dNOR(13)]. The extra chromosome 21 in the proband was maternal origin. The frequency of NOR chromosome association showed relatively high frequency in the mother and proband as compared to the controls. The result suggest that chromosome variants involving extra copies of NOR may indeed be involved in the meiotic nondisjunction of chromosome-21. 相似文献
34.
35.
Evangelia G. Kranias Ramesh C. Gupta Gyorgyi Jakab Hae Won Kim Nancy A. E. Steenaart Stephen T. Rapundalo 《Molecular and cellular biochemistry》1988,82(1-2):37-44
Summary Canine cardiac sarcoplasmic reticulum is phosphorylated by adenosine 3,5-monophosphate (cAMP)-dependent and by calcium · calmodulin-dependent protein kinases on a 27 000 proteolipid, called phospholamban. Both types of phosphorylation are associated with an increase in the initial rates of Ca2+ transport by SR vesicles which reflects an increased turnover of elementary steps of the calcium ATPase reaction sequence. The stimulatory effects of the protein kinases on the calcium pump may be reversed by an endogenous protein phosphatase, which can dephosphorylate both the CAMP-dependent and the calcium · calmodulin-dependent sites on phospholamban. Thus, the calcium pump in cardiac sarcoplasmic reticulum appears to be under reversible regulation mediated by protein kinases and protein phosphatases. 相似文献
36.
Oxidative decarboxylation of [1-14C]pyruvate was studied in primary cultures of neurons and of astrocytes. The rate of this process, which is a measure of carbon flow into the tricarboxylic acid (TCA) cycle and which is inhibited by its end product, acetyl CoA, was determined under conditions which would either elevate or reduce the components of the malate-aspartate shuttle (MAS). Addition of aspartate (1 mM) was found to stimulate pyruvate decarboxylation in astrocytes whereas addition of glutamate (or glutamine) had no effect. Since aspartate is a precursor for extramitochondrial malate, and thus intramitochondrial oxaloacetate, whereas glutamate and glutamine are not, this suggests that an increase in oxaloacetate level stimulates TCA cycle activity. Conversely, a reduction of the glutamate content by 3 mM ammonia, which might reduce exchange between glutamate and aspartate across the mitochondrial membrane, suppressed pyruvate decarboxylation. This effect was abolished by addition of glutamate or glutamine or exposure to methionine sulfoximine (MSO). These findings suggest that impairment of MAS activity by removal of MAS constituents decreases TCA cycle activity whereas replenishment of these compounds restores the activity of the TCA cycle. No corresponding effects were observed in neurons. 相似文献
37.
The effect of intraperitoneal administration of L-methionine-DL-sulphoximine (MSI) was studied on branched-chain amino acid transaminases (BCAA-T) in different regions of rat brain and in liver. Administration of an acute dose of MSI (300 mg/kg body weight) resulted in a significant decrease in leucine aminotransferase activity in cerebral cortex, cerebellum, and brain-stem, while the activity of isoleucine aminotransferase was enhanced in hippocampus, corpus striatum, brain stem, and midbrain. Activities of both these enzymes changed marginally or remained unaltered in other regions of the brain. Valine aminotransferase showed a significant decrease in all the regions of the brain except in cerebellum. Following the administration of a sub-acute dose of MSI (150 mg/kg body wt.), the activities of the three BCAA aminotransferases were found to be enhanced in all regions of the brain. The results are discussed in relation to the utilization of BCAA for the production of glutamate and glutamine in hyperammonemia. 相似文献
38.
Sirintornthep Towprayoon Badal Chandra Saha Yusaku Fujio Seinosuke Ueda 《Applied microbiology and biotechnology》1988,29(2-3):289-291
Summary The effect of an inhibitory factor (IF) fromAspergillus niger 19 on raw starch digestion by pure glucoamylase I of blackAspergillus, pure glucoamylae ofRhizopus niveus, bacterial -amylase, fungal -amylase and various combination was investigated. The IF caused higher inhibition of raw starch hydrolysis by the combined action of glucoamylase and fungal -amylase than of hydrolysis by the individual enzymes. A protein moiety of IF might play an active part in this inhibition phenomenon. The IF was bound to starch granules, preventing hydrolysis by the enzymes, and caused decreased raw starch hydrolysis yields. 相似文献
39.
K. Madhava Madyastha N. S. R. Krishna Murthy 《Applied microbiology and biotechnology》1988,28(4-5):324-329
Summary Incubation of acetates of geraniol, citronellol and linalool with Aspergillus niger resulted in their hydrolysis to corresponding alcohols which were further hydroxylated to their respective 8-hydroxy derivatives. In the case of linalyl acetate, besides linalool and 8-hydroxylinalool, small amounts of geraniol and -terpineol were also formed. Microsomes (105 000xg sediment) prepared from induced cells of A. niger were found to convert (1-3H)citronellol to 8-hydroxy citronellol in the presence of NADPH and O2. The pH optimum for the hydroxylase was found to be 7.6. 相似文献
40.
The prevalence and intensity of larval nematodes in fillets of Atlantic cod, Gadus morhua, were examined and compared with similar data from a previous survey conducted about 30 yr ago. Anisakis simplex occurred more often in the nape of the fillet, whereas Pseudoterranova decipiens was the predominant species in napeless fillets. The results suggest an increase in both the prevalence and intensity of P. decipiens in fillets of cod, especially those originating from the Gulf of St. Lawrence and coastal Nova Scotia. 相似文献