全文获取类型
收费全文 | 3468篇 |
免费 | 362篇 |
国内免费 | 172篇 |
出版年
2023年 | 15篇 |
2022年 | 37篇 |
2021年 | 89篇 |
2020年 | 82篇 |
2019年 | 86篇 |
2018年 | 97篇 |
2017年 | 101篇 |
2016年 | 119篇 |
2015年 | 193篇 |
2014年 | 181篇 |
2013年 | 264篇 |
2012年 | 245篇 |
2011年 | 251篇 |
2010年 | 187篇 |
2009年 | 162篇 |
2008年 | 179篇 |
2007年 | 175篇 |
2006年 | 152篇 |
2005年 | 144篇 |
2004年 | 127篇 |
2003年 | 113篇 |
2002年 | 103篇 |
2001年 | 92篇 |
2000年 | 84篇 |
1999年 | 70篇 |
1998年 | 37篇 |
1997年 | 35篇 |
1996年 | 23篇 |
1995年 | 31篇 |
1994年 | 21篇 |
1993年 | 17篇 |
1992年 | 56篇 |
1991年 | 36篇 |
1990年 | 34篇 |
1989年 | 38篇 |
1988年 | 31篇 |
1987年 | 27篇 |
1986年 | 20篇 |
1985年 | 32篇 |
1984年 | 19篇 |
1983年 | 20篇 |
1982年 | 10篇 |
1981年 | 9篇 |
1980年 | 14篇 |
1979年 | 9篇 |
1978年 | 17篇 |
1975年 | 11篇 |
1974年 | 12篇 |
1973年 | 20篇 |
1972年 | 12篇 |
排序方式: 共有4002条查询结果,搜索用时 15 毫秒
91.
E-cadherin expression during the differentiation of human trophoblasts 总被引:14,自引:0,他引:14
C Coutifaris L C Kao H M Sehdev U Chin G O Babalola O W Blaschuk J F Strauss 《Development (Cambridge, England)》1991,113(3):767-777
92.
Oscar Lazcano Jorge Bilbao Robert S. Beissner Martha Vandiver Chin Yang Li 《Biotechnic & histochemistry》1992,67(1):14-20
Permanent preparations of air dried synovial fluids were prepared by staining calcium compounds with alizarin red S stain; each slide was coverslipped with Permount. Variables studied were: (a) concentration of the solution of alizarin red S, (b) pH of staining solution, (c) time of incubation in staining solution and aqueous and ethanolic content of staining solution. The staining effect of each solution was tested on calcium pyrophosphate dihydrate, calcium oxalate, apatite and monosodium urate (MSU). Of all the solutions, best results were obtained with 0.25% alizarin red S in 50% ethanol at pH 7.0 for 30 min. With this solution, the calcium-containing compounds were well stained. MSU did not stain and still preserved negative birefringence on polarizaton. Fixation of smears with ethanol served a double purpose: It fixed the slides without dissolving or removing MSU or the calcium compounds, yet it did dissolve five corticosteroids commonly used for intra-articular injection which may interfere with interpretation of compensated polarized light microscopy of synovial fluids. 相似文献
93.
A nuclear factor that enhances binding of thyroid hormone receptors to thyroid hormone response elements 总被引:24,自引:0,他引:24
Recent studies from this laboratory have demonstrated the presence of thyroid hormone response elements (TREs) in the 5'-flanking region of the rat alpha and TSH beta subunit genes. Using an avidin-biotin complex DNA binding assay, we have shown that these TREs bind the thyroid hormone (T3) receptor present in nuclear extracts of GH3 cells, as well as the in vitro synthesized Hc-erbA beta, which has been identified as a member of the family of T3 receptors. The binding of Hc-erbA beta to the alpha subunit TRE can be enhanced 3-4-fold by including GH3 nuclear extract in the binding assay. Binding to the TRE present in the TSH beta gene or the rat growth hormone gene was similarly enhanced, although to a lesser degree. The enhanced binding activity is trypsin-sensitive and heat labile, and is not reproduced by the addition of histones, bovine serum albumin, or cytosol instead of nuclear extract. Gel exclusion chromatography suggests a molecular size of approximately 65,000 Da. This protein, which is present in several different cell types, is also able to complement binding of the rat erbA alpha-1 and the pituitary-specific erbA beta-2 forms of the receptor. These data suggest that the binding of the T3 receptor to a TRE is augmented by another nuclear protein, which may be involved in the mechanism of action of thyroid hormone. 相似文献
94.
Somatic embryos in liquid culture can serve as a mass cloning system in a plant propagation program. A quantitative formulation of embryo development obtained from cell suspension cultures is used to develop a segregated kinetic model. The model is based on standard classification schemes as previously developed by plant physiologists. Dependent variables include carbohydrate concentrations (sucrose, fructose, and glucose) and biomass apportioned among the inoculum (free single cells, cell clusters), normal developmental stages, and aberrant cell and embryo types. Good agreement between the model and experimental results is indicated and allows for a rigorous approach to media optimization and reactor scaleup for embryo formation. 相似文献
95.
W E Collins P G Contacos J C Skinner A Y Huong W Chin 《The Journal of parasitology》1982,68(5):877-883
The Cambodian I strain of Plasmodium falciparum, originally from Kampuchea was adapted for development in three different types of Aotus monkeys. High-level parasitemias were readily produced in splenectomized Colombian A. trivirgatus griseimembra monkeys. Initially, only minimal parasitemias developed in A. t. trivirgatus monkeys from Colombia. However, in one animal, adaptation occurred and high-level parasitemias were obtained during the second recrudescence of the infection. Passage to other A. t. trivirgatus monkeys indicated that the parasite was well adapted for development in splenectomized animals; low to moderate parasitemias were still produced in intact animals. This line of the parasite produced high level parasitemias when inoculated into splenectomized Aotus monkeys from Peru. Infections in Anopheles freeborni mosquitoes were obtained as late as the 7th passage in A. t. griseimembra monkeys and as late as the 7th recrudescence of the infection in an individual monkey (348 days after inoculation). The sporogonic cycle was completed in An. freeborni mosquitoes, and one transmission to an A. t. griseimembra monkey via the bites of infected mosquitoes was obtained. 相似文献
96.
Abstract: Mouse brain tubulin was analyzed on isoelectric focusing gels. High-resolution gels utilizing Bio-Rad ampholytes (pH 4-6) revealed 5-6 bands in the region corresponding to the α-subunit of tubulin and 10 or more for the β-subunit. The same general banding pattern was observed regardless of the method of preparation of the tubulin. Two species prominent in the brains of immature mice, α6 and β2, virtually disappeared during maturation, while species β6 to β10 appeared. No significant changes from the mature pattern were seen during aging (examined at 12, 23, and 30 months of age). 相似文献
97.
Epidemic hemorrhagic fever in Hubei Province, The People's Republic of China: a clinical and serological study 总被引:1,自引:0,他引:1
M S Cohen J Casals G D Hsiung H E Kwei C C Chin H C Ge C M Hsiang P W Lee C J Gibbs D C Gajdusek 《The Yale journal of biology and medicine》1981,54(1):41-55
Between July 1975 and April 1980, 71 patients were admitted to the Second Attached Hospital of Hubei Provincial Medical College in Wuchang with the diagnosis of epidemic hemorrhagic fever (EHF). The clinical course among these patients was similar to that described for patients with Korean hemorrhagic fever, and hemorrhagic fever with renal syndrome of the U.S.S.R. The overall mortality was 11.2 percent. Sera obtained from some of these patients as well as from patients admitted to the First Attached Hospital of Hubei Provincial Medical College were tested against an antigen associated with Korean hemorrhagic fever and showed exceedingly high antibody titers. We conclude that EHF in Central China represents the same or a closely related disease process as Korean hemorrhagic fever. 相似文献
98.
99.
The Ames assay employing Salmonella typhimurium TA100 and TA98 was used to investigate potential interactions between aflatoxin B1 (AFB1) and the phenolic antioxidants butylated hydroxytoluene, butylated hydroxyanisole, and propyl gallate. AFB1 doses were within the linear response range, and the antioxidants were used at levels of 0 to 50 micrograms per plate. All three antioxidants were nonmutagenic in either bacterial tester strain, with or without the hepatic S-9 enzyme preparation; toxic effects were observed at doses higher than 20 micrograms per plate. Butylated hydroxytoluene and butylated hydroxyanisole substantially increased AFB1-induced mutagenesis in the two tester strains with microsomal activation. The addition of 5 to 20 micrograms of butylated hydroxytoluene or hydroxyanisole to 5 to 20 ng of AFB1 per plate caused more than a twofold increase in the number of His+ revertants. Addition of propyl gallate resulted in only a moderate increase in the number of revertants. Whereas several anticarcinogenic and antimutagenic effects by phenolic antioxidants have been reported, particularly in studies with polycyclic aromatic hydrocarbons, the enhancement of mutagenic potency of AFB1 by these compounds suggests a specificity with respect to the chemical nature of AFB1. 相似文献
100.
M A Handel J Papaconstantinou D P Allison E M Julku E T Chin 《Developmental biology》1973,35(2):240-249
During the mid to late 4th instar period of larval development, the mitochondria of Rhynchosciara spermatocytes undergo highly characteristic morphological changes. In late meiosis the enlarged mitochondria fuse to form a single mitochondrial element which will ultimately extend the length of the spermatid tail. Our studies have shown that synthesis of a circular DNA occurs during this period of mitochondrial “differentiation.” This DNA has a density of 1.681 g/cm3; and its synthesis cannot be detected in somatic tissues such as salivary gland, fat body, or gastric cecum. From analysis of DNA extracted from mitochondrial pellets, we have shown that the circular DNA is associated with the mitochondria. The contour length of the mitochondrial DNA is 9 μm, equivalent to a molecular weight of 18 × 106. Although most metazoan mitochondrial DNAs exhibit contour lengths of approximately 5 μm (10 × 105 daltons), there is no extractable 5 μm circular DNA in these spermatocytes. Therefore, we conclude that either Rhynchosciara spermatocytes possess a distinct 9 μm mitochondrial DNA or that the spermatocyte mitochondrial DNA represents dimers of 5 μm monomers. 相似文献