全文获取类型
收费全文 | 117949篇 |
免费 | 6646篇 |
国内免费 | 28篇 |
专业分类
124623篇 |
出版年
2021年 | 1266篇 |
2019年 | 1008篇 |
2018年 | 1640篇 |
2017年 | 1586篇 |
2016年 | 2157篇 |
2015年 | 2563篇 |
2014年 | 3008篇 |
2013年 | 4058篇 |
2012年 | 4677篇 |
2011年 | 4638篇 |
2010年 | 3371篇 |
2009年 | 2933篇 |
2008年 | 4125篇 |
2007年 | 4092篇 |
2006年 | 3802篇 |
2005年 | 3672篇 |
2004年 | 3564篇 |
2003年 | 3394篇 |
2002年 | 3192篇 |
2001年 | 4555篇 |
2000年 | 4294篇 |
1999年 | 3421篇 |
1998年 | 1281篇 |
1997年 | 1198篇 |
1996年 | 1068篇 |
1995年 | 957篇 |
1994年 | 944篇 |
1993年 | 950篇 |
1992年 | 2548篇 |
1991年 | 2539篇 |
1990年 | 2575篇 |
1989年 | 2301篇 |
1988年 | 2153篇 |
1987年 | 2066篇 |
1986年 | 1879篇 |
1985年 | 1898篇 |
1984年 | 1588篇 |
1983年 | 1357篇 |
1982年 | 1013篇 |
1979年 | 1486篇 |
1978年 | 1165篇 |
1977年 | 1053篇 |
1976年 | 1007篇 |
1975年 | 1182篇 |
1974年 | 1286篇 |
1973年 | 1356篇 |
1972年 | 1198篇 |
1971年 | 1058篇 |
1970年 | 941篇 |
1969年 | 966篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
131.
Royal jelly: can it reduce physiological strain of growing rabbits under Egyptian summer conditions? 总被引:1,自引:0,他引:1
Elnagar SA Elghalid OA Abd-Elhady AM 《Animal : an international journal of animal bioscience》2010,4(9):1547-1552
Exposure of growing rabbits to heat stress during summer adversely affects their performance leading to major production losses. A total number of 48 rabbits, unsexed V-line weaned rabbits, were randomly divided into four experimental groups, temperature ranged from high at 32°C to low at 23°C. Animals of the 2nd, 3rd and 4th group were individually orally given 200, 400 or 800 mg royal jelly (RJ)/kg BW once a week, respectively, to evaluate RJ ability to reduce physiological strain resulted from heat stress. Weekly BW gain increased by 10.4, 11.8 and 10.8%, and feed conversion ratio was significantly improved by 20, 24 and 18% with RJ treatments. Serum total protein, albumin and globulin increased, whereas serum total lipids, cholesterol and triglycerides decreased with RJ treatments. Creatinine was reduced by 21, 30 and 18% and uric acid by 14, 25 and 18% compared with the heat stressed control with the three doses of RJ. Glucose level increased significantly to reach 116, 125, and 120% of heat stressed control. Calcium, phosphorus and alkaline phosphatase increased significantly with RJ treatments indicating the occurrence of active bone deposition. Thyroid hormone levels increased significantly to reach 108, 111, and 112% of heat stressed control rabbits with the three doses of RJ, counteracting the hypothyroid state resulted from heat stress. It can be concluded that RJ administration to heat stressed growing rabbits can reduce physiological strain resulted from heat stress. 相似文献
132.
Since their discovery in the early 1980s, viruses that infect the third domain of life, the Archaea, have captivated our attention because of their virions' unusual morphologies and proteins, which lack homologues in extant databases. Moreover, the life cycles of these viruses have unusual features, as revealed by the recent discovery of a novel virus egress mechanism that involves the formation of specific pyramidal structures on the host cell surface. The available data elucidate the particular nature of the archaeal virosphere and shed light on questions concerning the origin and evolution of viruses and cells. In this review, we summarize the current knowledge of archeoviruses, their interaction with hosts and plasmids and their role in the evolution of life. 相似文献
133.
A. Rogel Y. Bromberg O. Sperling E. Zoref-Shani 《Nucleosides, nucleotides & nucleic acids》2013,32(9-11):1283-1286
We have demonstrated before that exposure of neuronal cultures to poisoning by iodoacetic acid (IAA) followed by “reperfusion” (IAA-R insult), results in severe cytotoxicity, which could be markedly attenuated by prior activation of the adenosine A1 receptors. We also have demonstrated that adenosine activates a signal transduction pathway (STP), which involves activation of PKCε and opening of KATP channels. Here, we provide proof for the involvement also of phospholipase C (PLC) in the neuronal protective adenosine-activated STP. R-PIA, a specific A1 adenosine receptor agonist, was found to enhance neuronal PLC activity and protect against the IAA-R insult. The PLC inhibitor U73122, abrogated both R-PIA-induced effects. These results demonstrate that activation of PLC is a vital step in the neuronal protective adenosine-induced STP. 相似文献
134.
Populations of macrophages and neutrophils in the uterus are under the control of the female sex steroids estrogen and progesterone (P4). Their influx is induced by estrogen, while P4 can both stimulate and inhibit leukocyte influx depending on the timing of P4 with respect to estrogen. Regulation of leukocytes has been implicated in changes in uterine immune responses during the estrous cycle, pregnancy, and implantation. This work demonstrates that P4 given concurrently with estrogen to ovariectomized mice for 4 days antagonizes the ability of estrogen to recruit macrophages and neutrophils into the mouse uterus. Using progesterone receptor knockout (PRKO) mice, we show that this effect is dependent on progesterone receptors (PR). In the absence of PR, neutrophils recruited by estrogen were found to be degranulated, partially explaining the edema that is observed with long-term treatment of PRKO mice with estrogen and P4. Populations of B lymphocyte cells were shown to be unchanged by estrogen and P4 treatment in both wild-type and PRKO mice. The neutrophil chemotactic chemokine MIP-2 was examined for down-regulation by P4 but was found to be unaffected by hormonal treatment. Together, these observations demonstrate that PR has a strong anti-inflammatory role in the mouse uterus when estrogen and P4 are present together. 相似文献
135.
Haag M Kearns SD Magada ON Mphata PR Claassen N Kruger MC 《Prostaglandins & other lipid mediators》2001,66(1):53-63
Duodenal ion transport processes are supported by ATPase enzymes in basolateral membranes of the enterocyte. In vivo studies have shown that long term n-6 poly-unsaturated fatty acid (PUFA) supplementation in rats causes increases in intestinal Ca absorption, coupled with a higher total calcium balance and bone calcium content. The present in vitro study was undertaken to test the effect of arachidonic acid (AA), a highly unsaturated (and thus physiologically potent) member of the n-6 PUFA family, on ATPases in enterocyte basolateral membranes isolated with a sorbitol density gradient procedure. This paper presents results which show that AA inhibits Na+,K+-ATPase in a dose-dependent manner (-67% of basal activity at a concentration of 30 microg/ml, P < 0.005) but that this effect is not mediated by protein kinase C, as shown by the use of the protein kinase C blocker calphostin (0.5 microM). Indomethacin (IDM) at 0.1 mM, a cyclo-oxygenase blocker, could also not reverse the inhibitory effect of AA on Na+,K+-ATPase. Ca2+-ATPase, on the other hand, is not affected significantly (-10%, P > 0.05) by arachidonic acid at 30 microg/ml. 相似文献
136.
G. F. Makhaeva N. V. Kovaleva S. V. Lushchekina E. V. Rudakova N. P. Boltneva A. N. Proshin B. V. Lednev I. V. Serkov S. O. Bachurin 《Doklady. Biochemistry and biophysics》2018,483(1):369-373
Using the acylation reaction with tosyl chloride of N-aminopropyl analogues of tacrine and its cyclic homologues with different size of the aliphatic cycle (5–8), we synthesized a number of new derivatives of p-toluenesulfonamide. It is shown that the synthesized hybrid compounds of tacrine and p-toluenesulfonamide are effective inhibitors of acetylcholinesterase (AChE) and butyrylcholinesterase (BChE) with the preferential inhibition of BChE. They also displace propidium from the peripheral anionic site of the electric eel AChE (Electrophorus electricus). The characteristics of the efficiency and selectivity of cholinesterase inhibition by the test compounds were confirmed by the results of molecular docking. 相似文献
137.
The nucleotide sequence of the G6-amylase gene from alkalophilic Bacillus sp. H-167 was determined. The open reading frame of the gene consisted of 2865 base pairs, encoding 955 amino acids. The NH2-terminal amino acid sequence analysis of the G6-amylase indicated that the enzyme had a single peptide of 33 amino acid residues and the mature enzyme was composed of 922 amino acids, giving a molecular mass of 102,598. Identity of the NH2-terminal amino acid sequences among each component of the multiform G6-amylase suggested the proteolytic processing of the COOH-terminal side of the enzyme. The DNA sequence and the deduced amino acid sequence of the G6-amylase gene showed no homology with those of other bacterial alpha-amylases although the consensus amino acid sequences of the active center were well conserved. 相似文献
138.
Charles C. Ngugi Julius O. Manyala Murithi Njiru Chrisestom M. Mlewa 《African Journal of Ecology》2009,47(4):606-613
A study on some biological parameters of the mountain catfish, Amphilius uranoscopus Pfeffer 1889 (Silurifomes: Amphiliidae), was carried out in the Thego stream on the slopes of Mount Kenya from February to December 2002. Physical and chemical profiles of the Thego show that the water quality parameters is typical of high altitude streams with temperatures rarely exceeding 18°C, DO ranging from 7.9 to 8.2 mg l?1 and relatively high conductivity (97–137 μS cm?1) typical of perturbed lotic environments. A total of 1010 fish were caught by an electro‐fisher, with sizes ranging between 8 and 24 cm fork length. The population structure had a unimodal distribution with maxima at 14–16 cm. The length–weight relationship showed relatively narrow range in the slope ranging from 2.61 in April to 2.98 in February 2002, thereby suggesting isometric growth pattern. The fitted growth pattern of A. uranoscopus showed an asymptotic length (L∞) of 28.5 cm and a growth curvature (K) of 0.56 year?1 resulting in an estimated natural mortality coefficient (M) of 0.90 year?1. The Fulton’s condition factor (K) was also relatively stable with a peak in April (0.92 ± 0.21) and lowest value in June (0.86 ± 0.10). As A. uranoscopus is not under commercial exploitation, the seemingly depressed population is possibly attributed to the introduced exotic rainbow trout that heavily predates on the species and environmental perturbations arising from changes in land use. The implications of such changes on A. uranoscopus are discussed. 相似文献
139.
Jane E. Greig Philipp A. du Cros Clair Mills Wilfred Ugwoeruchukwu Andrew Etsetowaghan Adetola Grillo Adetoro Tayo-Adetoro Kunle Omiyale Tim Spelman Daniel P. O’Brien 《PloS one》2013,8(8)