全文获取类型
收费全文 | 3984篇 |
免费 | 249篇 |
国内免费 | 4篇 |
专业分类
4237篇 |
出版年
2023年 | 21篇 |
2022年 | 53篇 |
2021年 | 94篇 |
2020年 | 64篇 |
2019年 | 73篇 |
2018年 | 122篇 |
2017年 | 91篇 |
2016年 | 166篇 |
2015年 | 216篇 |
2014年 | 214篇 |
2013年 | 320篇 |
2012年 | 343篇 |
2011年 | 325篇 |
2010年 | 219篇 |
2009年 | 144篇 |
2008年 | 241篇 |
2007年 | 233篇 |
2006年 | 219篇 |
2005年 | 196篇 |
2004年 | 169篇 |
2003年 | 152篇 |
2002年 | 151篇 |
2001年 | 31篇 |
2000年 | 17篇 |
1999年 | 30篇 |
1998年 | 34篇 |
1997年 | 28篇 |
1996年 | 24篇 |
1995年 | 24篇 |
1994年 | 19篇 |
1993年 | 19篇 |
1992年 | 28篇 |
1991年 | 17篇 |
1990年 | 11篇 |
1989年 | 12篇 |
1988年 | 12篇 |
1987年 | 9篇 |
1986年 | 11篇 |
1985年 | 8篇 |
1984年 | 7篇 |
1983年 | 11篇 |
1982年 | 7篇 |
1981年 | 5篇 |
1980年 | 3篇 |
1979年 | 6篇 |
1978年 | 4篇 |
1977年 | 6篇 |
1976年 | 4篇 |
1975年 | 5篇 |
1974年 | 4篇 |
排序方式: 共有4237条查询结果,搜索用时 0 毫秒
141.
Bovine seminal ribonuclease (BS-RNase), a dimeric homologue of RNase A, cleaves both single- and double-stranded RNA and inhibits the growth of tumor cells. Its catalytic activity against double-stranded RNA, either homopolymeric ([3H]polyA/polyU) or mixed sequence, is enhanced by bovine or human recombinant interferon-γ (IFN-γ). Activation is seen with as little as 4–10 interferon units per assay. Enhancing the degradation of double-stranded RNA, an intermediate in the growth cycle of many viruses, could contribute to IFN-γ's ability to control cell growth and induce an antiviral state. 相似文献
142.
Klösch B Fürst W Kneidinger R Schuller M Rupp B Banerjee A Redl H 《Biotechnology letters》2005,27(20):1559-1564
Rat bone morphogenetic protein-4 (rBMP-4) cDNA was cloned from rat osteoblasts by RT-PCR and expressed in E. coli. Monomeric, dimeric and polymeric forms of recombinant rat BMP-4 (rrBMP-4) were obtained from inclusion bodies after solubilization
with urea. The dimer was separated from the remaining polymer and host cell contaminants using size exclusion chromatography.
Furthermore, purified rrBMP-4 was stabilized at low urea concentration (40 mm) and at pH 8.5 through the addition of bovine serum albumin. Both, rrBMP-4 dimer and polymer were biologically active as
tested by the induction of alkaline phosphatase activity in MC3T3-E1 cells. 相似文献
143.
144.
The leaves of necrotic hybrid of wheat ( Triticum aestivum L.) exhibited high superoxide content associated with increased lipid peroxidation and membrane damage in earlier studies (Khanna-Chopra et al. 1998, Biochem Biophys Res Commun 248: 712–715; Dalal and Khanna-Chopra 1999, Biochem Biophys Res Commun 262: 109–112). In the present study, we investigated the activities of the antioxidant enzymes in the leaves of necrotic wheat hybrids, Kalyansona×C306 (K×C) and WL711×C306 (WL×C) and their parents at different developmental stages. The K×C hybrid exhibited more severe necrosis than WL×C. In K×C, superoxide dismutase (SOD) activity showed no increase over the parents, while WL×C showed an early increase, but it was possibly insufficient to scavenge increased superoxide. Activities of guaiacol peroxidase, ascorbate peroxidase and glutathione reductase were enhanced, while catalase exhibited a decrease in activity, with the appearance of visible necrosis in both the hybrids. The isozyme profile of the antioxidant enzymes was similar in the hybrids and their parents. One existing isoform of guaiacol peroxidase showed an early appearance in the hybrid and increased in intensity with the progression of necrosis. The results reveal a differential response of antioxidant enzymes in necrotic wheat hybrids as compared to their parents. The response differed in magnitude at developmental stages of the leaves, which might be related to the intensity of necrosis expressed by the hybrids. 相似文献
145.
Subject Index
Subject Index to Volume 24 相似文献146.
Duplex Doppler sonography has been recognized as a noninvasive method to evaluate hemodynamic features of renal blood in renal and intrarenal arteries in patients with various renal diseases. The significance of duplex Doppler sonography in the evaluation of renal vascular resistance in glomerular diseases has not yet been clearly determined. The aim of the present study was to evaluate renal vascular resistance in patients with glomerular diseases by measuring intrarenal arterial resistance (RI) and to correlate RI with renal functional tests and other clinical and laboratory data. The Doppler parameters were also correlated with histopathological findings in the kidney which underwent the percutaneous biopsy. Duplex Doppler sonography was used to measure RIs in intrarenal arteries in 50 patients with glomerular diseases and 60 age-matched control subjects. The renal vascular resistance index (RI) was determined by the use of Doppler sonography. The mean RI in 50 patients with glomerular diseases was 0.68 +/- 0.09, which was statistically significantly higher than in 60 control subjects (the mean RI was 0.596 +/- 0.035). In a group of patients with membranoproliferative glomerulonephritis the mean RI was 0.817 +/- 0.624 which was statistically significantly higher than in other groups of glomerulonephritis. The renal vascular (resistance) RI significantly correlated with serum creatinine, creatinine clearance and beta2 microglobulin. Qualitative duplex sonography measure of renal arterial resistance-resistive index does not appear to be reliable in distinguishing different types of glomerulonephritis. 相似文献
147.
PknH, a transmembrane Hank's type serine/threonine kinase from Mycobacterium tuberculosis is differentially expressed under stress conditions 总被引:1,自引:0,他引:1
Sharma K Chandra H Gupta PK Pathak M Narayan A Meena LS D'Souza RC Chopra P Ramachandran S Singh Y 《FEMS microbiology letters》2004,238(1):107-113
148.
Microarray analyses of gene expression during adventitious root development in Pinus contorta 总被引:2,自引:0,他引:2 下载免费PDF全文
Brinker M van Zyl L Liu W Craig D Sederoff RR Clapham DH von Arnold S 《Plant physiology》2004,135(3):1526-1539
149.
Determinations of intracellular [Ca(2+)](i) during ischemia using fluorescent indicators are hampered by overlapping cellular autofluorescence (AF), which largely depends on NADH. If Ca(2+) is to be determined under different kinds of ischemia, signal separation merits special attention. We used triple wavelength excitation fluorescence to separate autofluorescence from [Ca(2+)]-dependent fura-2 fluorescence. Excitation at 360 nm served as third, Ca(2+)-insensitive wavelength. Using an appropriate evaluation procedure, we separated Ca(2+)-dependent signals from autofluorescence which is semiquantitatively associated with NADH, an indicator of the cellular redox state. We compared changes of [Ca(2+)](i) in isolated hearts during ischemia following cardioplegic arrest with those after transient stop of nutritive perfusion. We observed [Ca(2+)] transients in spontaneously beating hearts, persisting during ischemic episodes, and an increase of mean [Ca(2+)](i). In contrast, cardioplegic arrest stopped periodical [Ca(2+)](i) transients and heart beats simultaneously. [Ca(2+)](i) remained at diastolic values, tended to decrease during the first minutes of cardioplegic arrest and then increased slowly. Autofluorescence increased under both conditions. During ischemia, this increase was faster than in cardioplegia experiments. It started after the last heart beat despite persisting perfusion. Our measurements demonstrate that rhythmical heart beat is essential for sufficient perfusion. Reduced [Ca(2+)](i) under cardioplegic arrest may influence metabolism. 相似文献
150.
We report the targeted mutagenesis of the murine iron regulatory protein (IRP)-1 and IRP2 genes, respectively, with a classical gene trap construct. Insertion of the targeting cassette into the second intron of either gene by homologous recombination interrupts their open reading frames near the N termini. Mice that are homozygous for the correctly modified IRP1 or IRP2 alleles, respectively, display a strong reduction (90%, IRP1(-/-)) or nondetectable levels (IRP2(-/-)) of the targeted proteins. Interestingly, the pre-mRNAs transcribed from the identical targeting cassettes are processed differently within the two different contexts. Detailed analysis of the respective products identifies the choice of alternative splice and 3' end processing sites in the same tissues in vivo. We discuss the implications for the understanding of RNA processing and for targeting strategies for functional genomics in the mouse. 相似文献