全文获取类型
收费全文 | 13555篇 |
免费 | 1040篇 |
国内免费 | 836篇 |
专业分类
15431篇 |
出版年
2024年 | 31篇 |
2023年 | 138篇 |
2022年 | 336篇 |
2021年 | 603篇 |
2020年 | 375篇 |
2019年 | 487篇 |
2018年 | 433篇 |
2017年 | 335篇 |
2016年 | 494篇 |
2015年 | 834篇 |
2014年 | 890篇 |
2013年 | 1059篇 |
2012年 | 1226篇 |
2011年 | 1045篇 |
2010年 | 640篇 |
2009年 | 576篇 |
2008年 | 777篇 |
2007年 | 610篇 |
2006年 | 615篇 |
2005年 | 491篇 |
2004年 | 414篇 |
2003年 | 347篇 |
2002年 | 292篇 |
2001年 | 269篇 |
2000年 | 222篇 |
1999年 | 220篇 |
1998年 | 157篇 |
1997年 | 127篇 |
1996年 | 135篇 |
1995年 | 130篇 |
1994年 | 117篇 |
1993年 | 96篇 |
1992年 | 135篇 |
1991年 | 117篇 |
1990年 | 82篇 |
1989年 | 102篇 |
1988年 | 60篇 |
1987年 | 48篇 |
1986年 | 58篇 |
1985年 | 64篇 |
1984年 | 18篇 |
1983年 | 24篇 |
1982年 | 28篇 |
1981年 | 12篇 |
1980年 | 25篇 |
1979年 | 20篇 |
1978年 | 16篇 |
1977年 | 19篇 |
1974年 | 9篇 |
1972年 | 13篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
71.
72.
用PCR方法扩增人微小纤溶酶原(Microplasmingen,mPlg)基因,再与表达载体重组.构造mPlg原核表达质粒并转化大肠杆菌。阳性克隆pSSE-mPlg经温度诱导表达,SDS-PAGE等方法证明表达产物的分子量约为29kDa。占全菌总蛋白的24%左右,并在菌内形成包涵体。经半胱氨酸再氧化法和空气氧化法复性。表达产物r-mPlg经SK作用后显示纤溶活性。同时对蛋白质浓度、复性时间等因素对复性的影响进行了初步探讨。 相似文献
73.
HhaI and HpaII DNA methyltransferases bind DNA mismatches, methylate uracil and block DNA repair. 总被引:10,自引:7,他引:3 下载免费PDF全文
The hydrolytic deamination of 5-methylcytosine (5-mC) to thymine (T) is believed to be responsible for the high mutability of the CpG dinucleotide in DNA. We have shown a possible alternate mechanism for mutagenesis at CpG in which HpaII DNA-(cytosine-5) methyltransferase (M.HpaII) can enzymatically deaminate cytosine (C) to uracil (U) in DNA [Shen, J.-C., Rideout, W.M., III and Jones, P.A., Cell, 71, 1073-1080, (1992)]. Both the hydrolytic deamination of 5-mC and enzymatic deamination of C create premutagenic DNA mismatches (G:U and G:T) with the guanine (G) originally paired to the normal C. Surprisingly, we found that DNA-(cytosine-5) methyltransferases have higher affinities for these DNA mismatches than for their normal G:C targets and are capable of transferring a methyl group to the 5-position of U, creating T at low efficiencies. This binding by methyltransferase to mismatches at the recognition site prevented repair of G:U mismatches by uracil DNA glycosylase in vitro. 相似文献
74.
Cathy M. Tuck-Muller Harold Chen José E. Martínez Chuen-Cheh Shen Shibo Li Christine Kusyk Denise A. S. Batista Yogendra M. Bhatnagar Edmund Dowling Wladimir Wertelecki 《Human genetics》1995,96(1):119-129
Dicentrics are among the most common structural abnormalities of the human Y chromosome. Predicting the phenotypic consequences of different duplications and deletions of dicentric Y chromosomes is usually complicated by varying degrees of mosaicism (45,X cell lines), which may, in some cases, remain undetected. Molecular studies in patients with dicentric Y chromosomes have been few, and only two studies have attempted to determine the presence of SRY (the putative testis-determining factor gene). We report an 18-year-old female with short stature, amenorrhea, hirsutism, hypoplastic labia minora, and clitoromegaly who has a 45,X/46,X,idic(Y)(p11.32)/47,X,idic(Y)(p11.32),idic(Y) (p11.32) karyotype. Southern analysis using Y-specific probes (Y97, 2D6, 1F5, pY3.4) and polymerase chain reaction (PCR) analysis using primers for ZFY and SRY were positive for all loci tested, indicating that almost all of the Y chromosome was present. Our findings and an extensive review of the literature emphasize the importance of molecular analyses of abnormal Y chromosomes before any general conclusions can be reached concerning the relative effects of the Y-chromosome abnormality and mosaicism on sexual differentiation. 相似文献
75.
77.
78.
79.
A simple and sensitive method for the determination of polylysine in solution is described. Polylysine is quantitatively precipitated with trypan blue. The absorbance of unbound dye in the supernatant is inversely proportional to the concentration of this polyamino acid. The precipitation is identical for all sizes of polylysine of molecular weight 13,000 or higher, and is prevented by the addition of either polyanions or serum. The measurable range of polylysine hydrobromide is between 1 and 10 micrograms/ml, which is about 10-fold lower than that by the published methyl orange precipitation method. 相似文献
80.
The radiation sensitizers misonidazole (MISO) and desmethylmisonidazole (DMM) can produce central and peripheral neuropathy in patients and laboratory animals. Behavioral and pathological investigations have indicated that in the central nervous system this primarily involves the cochlear and vestibular systems. Nitroimidazoles can also interfere with glycolysis in vitro under aerobic and anaerobic conditions. In the present work we have studied the effect of MISO or DMM on lactate production and glucose utilization in mouse brain. It is observed that these compounds result in a 25% inhibition of lactate production in brain slices relative to the control at a 10 mM level. Additionally, MISO (1.0 mg/g/day) or DMM (1.4 mg/g/day) were administered daily (oral) for 1, 4, 7, or 14 days to examine the effect of these two drugs on the regional glucose utilization in C3Hf mouse brain. Five microcuries of 2-deoxy[14C]glucose was given following the last drug dose and autoradiographs of serial brain sections were made and analyzed by a densitometer. Following a single dose of either MISO or DMM, no significant differences in glucose uptake were observed when compared with controls. However, following 4, 7, and 14 doses the rate of glucose utilization was significantly reduced in the intoxicated animals. Larger reductions were measured in specific regions including the posterior colliculus, cochlear nuclei, vestibular nuclei, and pons with increasing effects observed at later stages. These results share a degree of correspondence with the regional brain pathology produced by these nitroimidazoles. 相似文献