全文获取类型
收费全文 | 2025篇 |
免费 | 211篇 |
出版年
2022年 | 24篇 |
2021年 | 46篇 |
2020年 | 17篇 |
2019年 | 26篇 |
2018年 | 36篇 |
2017年 | 29篇 |
2016年 | 48篇 |
2015年 | 65篇 |
2014年 | 76篇 |
2013年 | 109篇 |
2012年 | 158篇 |
2011年 | 138篇 |
2010年 | 96篇 |
2009年 | 83篇 |
2008年 | 102篇 |
2007年 | 128篇 |
2006年 | 105篇 |
2005年 | 116篇 |
2004年 | 109篇 |
2003年 | 86篇 |
2002年 | 92篇 |
2001年 | 28篇 |
2000年 | 26篇 |
1999年 | 25篇 |
1998年 | 17篇 |
1997年 | 21篇 |
1996年 | 18篇 |
1995年 | 18篇 |
1994年 | 12篇 |
1992年 | 31篇 |
1991年 | 22篇 |
1990年 | 19篇 |
1989年 | 13篇 |
1988年 | 15篇 |
1987年 | 17篇 |
1986年 | 17篇 |
1985年 | 10篇 |
1984年 | 18篇 |
1983年 | 19篇 |
1982年 | 12篇 |
1981年 | 15篇 |
1979年 | 9篇 |
1978年 | 10篇 |
1977年 | 11篇 |
1976年 | 11篇 |
1975年 | 9篇 |
1974年 | 19篇 |
1973年 | 13篇 |
1971年 | 14篇 |
1968年 | 10篇 |
排序方式: 共有2236条查询结果,搜索用时 15 毫秒
31.
Marina A. Sukoyan Sergei Y. Vatolin Alevtina N. Golubitsa Antonina I. Zhelezova Lora A. Semenova Oleg L. Serov 《Molecular reproduction and development》1993,36(2):148-158
A characterization of cell lines that we derived from morulae (three lines), blastocysts (two lines), and the inner cell mass (ICM) is given. The karyotype of all the lines was normal; the genotype of four lines was XX, and four lines were genotypically XY. The pluripotencies and commitment status of the derived lines were estimated. First, there were not less than two-thirds of cells in the populations of the lines derived from morulae and the lCM with both Xs active; 70–100% of cells of the blastocyst-derived lines had one of the Xs in an inactive state. The activity of glucose-6-phosphate dehydrogenase (G6PD) in the lines (genotype XX) derived from morulae and ICM was found to be twofold higher than in lines with genotype XY, and G6PD activity was the same in the blastocyst-derived XX lines and XY lines. Second, when injected intraperitoneally into athymic mice, morulae- and ICM-derived cells gave rise to simple and complex embryoid bodies (EB) resembling to typical “cystic” mouse EBs. Third, when injected subcutaneously to athymic mice, the ICM- or morula-derived cells gave rise to typical teratomas containing derivatives of the three germ layers and components of organogenesis. Comparisons of cell lines of different derivations demonstrated that the pluripotencies of the ES cells derived from morulae or the ICM are higher than those of blastocyst derivation. © 1993 Wiley-Liss, Inc. 相似文献
32.
Stereoselectivity of the Chinese hamster ovary cell sialidase: sialoside hydrolysis with overall retention of configuration 总被引:1,自引:1,他引:0
The stereochemical course of enzymatic hydrolysis by the solublesialidase from Chinese hamster ovary cells, expressed as a recombinantprotein in insect Sf9 cells, was determined using proton nuclearmagnetic resonance spectroscopy. 4-Methyl umbelliferyl-N-acetylneuraminic acid was employed as substrate, and the stereoselectivityof the enzyme catalysis was ascertained by monitoring the H3axial and equatorial protons of the sialic acid product overthe reaction course. At both high (3 U) and low concentrations(1 U) of the enzyme, the alpha anomer of the sialic acid wasclearly observed as the initial reaction product. The correspondingbeta anomer of sialic acid appeared much later in the reaction,arising from mutarotation of the alpha anomer. Similar studieswere also carried out using the Salmonella typhimurium LT 2sialidase, a protein of similar size and substrate specificity.Both enzymes apparently cleave the alpha linked sialoside substratewith retention of configuration. Based on the observations ofa wide variety of other glycohydrolytic enzymes that have showna strong correlation of the stereoselectivity of catalysis withactive site topology (Gebler et al, J. Biol. Chem. 267, 1255912561,1992), the results obtained here suggest that the microbialand mammalian sialidases have a homologous active site architectureeven though the molecules do not share significant primary sequencesimilarities. sialidase NMR enzyme mechanism Chinese hamster 相似文献
33.
Oleg G. Manylov 《Acta zoologica》1995,76(1):1-6
For the first time, the phenomenon of regeneration is reported for the phylum Gastrotricha. Adult specimens of Turbanella sp. were transected transversely and events of regeneration were observed on the light microscopical level. In both anterior and posterior fragments the wound closure was completed I day after the operation, and in 3 days the epidermis was restored entirely. The dorsal commissure of the Y-organ was rebuilt soon after wound closure. In anterior fragments cut at any level of the intestine, caudal adhesive tubes were formed anew, following the species-specific pattern. In posterior fragments, and in both fragments if transected at a pharynx level, regeneration resulted in a complete wound healing, with no new adhesive tubes being observed. 相似文献
34.
Abstract Conditional cold-sensitive mutations in Era, an essential Escherichia coli GTPase, were isolated. Localized random polymerase chain reaction (PCR) mutagenesis employing Taq and T7 DNA polymerases under error prone amplification conditions was exploited to generate mutations in the era gene. A plasmid exchange technique was used to identify conditional cold-sensitive mutations in Era that give rise to defective cell growth below 30 °C. Three recessive missense mutations in Era, N26S, A156D, and E200K, were isolated. All three mutations are located at residues conserved in Era homologues from Streptococcus mutans and Coxiella burnetii . 相似文献
35.
36.
Rapid accumulation and disappearance of plasma membrane proteins during development of wild-type and mutant strains of Dictyostelium discoideum 总被引:8,自引:0,他引:8
Plasma membranes were purified from the cellular slime mold Dictyostelium discoideum at different developmental stages and the protein compositions compared. The protein components of the plasma membrane of vegetative cells are largely conserved during development. Specific morphogenetic events are accompanied by synthesis and accumulation of several new proteins which are subsequently lost as development progresses. Proteins with apparent molecular weights of 38,000, 36,500 and 10,000 to 12,000 rapidly accumulate during the first six hours of development and then disappear from the plasma membrane after 12 hours. Later in development, several new high molecular weight proteins are synthesized and appear in the membrane. The pattern of accumulation of membrane proteins in wild-type and mutant strains suggests that appearance of membrane proteins is linked to a dependent sequence of events. 相似文献
37.
38.
39.
We have investigated primary and secondary responses of mouse splenic T cells to strong mixed lymphocyte stimulating antigens controlled by theMls locus using MHC-identical mixtures of cells. Our studies show that strong primaryMls-locus specific responses involve recognition of self I-A antigens, since BUdR and light suicide or F1 into parent radiation bone-marrow chimeras both demonstrate a preference of unprimed F1 T cells to respond to Mis-locus antigens associated with one parent's MHC antigens. Furthermore, conventional anti-I-A antisera and monoclonal anti-I-A antibody both inhibitMls-locus responses in an MHC-specific manner. Finally, as is typical of T cells responding to I-A antigens or to nominal antigens associated with self I-A,Mlslocus responses are mediated by Lyt-1+, 2– cells. One striking finding in these studies was the very high frequency of cells capable of responding to Mls-locus antigens, the highest being 1/300 splenic T cells. This plus evidence for recruitment during primaryMls-locus responses may account for reports of a lack ofI-A restriction in secondary anti-Mls locus responses to strong Mls-locus antigens, a finding with which we concur. The possibility that these secondary responses between noncongenic strains of mice may be directed at other genetic loci is also discussed. These experiments leave open the question of the biological role of theMls-locus and of the very large number of T cells reactive to it.Abbreviations used in this paper MHC
Major histocompatibility complex
- MIg
Mouse immunoglobulin
- MLC
Mixed lymphocyte culture
- TCGF
T-cell growth factor 相似文献
40.
M R Lerner 《Journal of theoretical biology》1979,77(2):213-216
Uncommitted fibroblasts may exist (Kirkwood &; Holliday, 1975; Holliday, Huschtscha, Tarrant &; Kirkwood, 1977). I show that, even if such cells divide significantly faster than committed ones, the uncommitted cells would be overlooked if one uses current culture techniques. Some general guidelines for testing the model are outlined. Uncommitted cells would be useful in studying the biochemical mechanisms of aging and development. 相似文献