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91.
The anteroposterior character of mesoderm induced by a peptide growth factor (XTC-MIF) was tested by transplantation into host Xenopus gastrulae. Both retinoic acid and a homeodomain protein were able to override the anteriorizing effect of the growth factor. Microinjection of a posteriorly expressed homeobox mRNA can respecify anteroposterior identity, transforming head mesoderm into tail-inducing mesoderm. Unexpectedly, overexpression of XIHbox 6 protein in the transplanted cells, without addition of growth factors, caused the formation of tail-like structures. The cells overexpressing XIHbox 6 were able to recruit cells from the host into the secondary axis. The results suggest that vertebrate homeodomain proteins are part of the biochemical pathway leading to the generation of the body axis. 相似文献
92.
The objective of this study was to determine the effects of passive immunization against estradiol on the occurrence and timing of estrus, ovulation and fertilization rates and on early embryonic development in mice. Swiss Webster fermale mice were randomly assigned to one of the three treatment groups to be injected with 0.1 ml saline (control; n=15), 0.1 ml anti-estradiol antisera (high dose: n=17) or 0.1 ml antiestradiol antisera diluted 1:10 with saline (low dose; n=17) at seven weeks of age. Immediately after injection mice were placed with males and observed daily for the presence of vaginal plugs for 10 d. Three days after vaginal plugs were observed, mice were terminated and the uteri were removed and flushed to determine the number and quality of unfertilized ova and embryos. No differences were observed in the timing of vaginal plug formation, the proportion of mice with vaginal plugs, or the mean number of unfertilized ova or embryos collected from each treatment group. However, the proportion of excellent or good quality embryos was reduced in the high dosage treatment. It was concluded from this study that passive immunization of mice against estradiol did not increase the number of embryos obtained from mice and that a high dosage of antisera against estradiol reduced embryo quality. These results provide evidence that alterations in levels of estradiol may adversely affect embryonic development. 相似文献
93.
We have characterized the function of a new neurogenic locus, brainiac (brn), during oogenesis. Homozygous brn females lay eggs with fused dorsal appendages, a phenotype associated with torpedo (top) alleles of the Drosophila EGF receptor (DER) locus. By constructing double mutant females for both brn and top, we have found that brn is required for determining the dorsal-ventral polarity of the ovarian follicle. However, embryos from mature brn eggs develop a neurogenic phenotype which can be zygotically rescued if a wild-type sperm fertilizes the egg. This is the first instance of a Drosophila gene required for determination of dorsal-ventral follicle cell fates that is not required for determination of embryonic dorsal-ventral cell fates. The temperature-sensitive period for brn dorsal-ventral patterning begins at the inception of vitellogenesis. The interaction between brn and DER is also required for at least two earlier follicle cell activities which are necessary to establish the ovarian follicle. Prefollicular cells fail to migrate between each oocyte/nurse cell complex, resulting in follicles with multiple sets of oocytes and nurse cells. brn and DER function is also required for establishing and/or maintaining a continuous follicular epithelium around each oocyte/nurse cell complex. These brn functions as well as the brn requirement for determination of dorsal-ventral polarity appear to be genetically separable functions of the brn locus. Genetic mosaic experiments show that brn is required in the germline during these processes whereas the DER is required in the follicle cells. We propose that brn may be part of a germline signaling pathway differentially regulating successive DER-dependent follicle cell activities of migration, division and/or adhesion and determination during oogenesis. These experiments indicate that brn is required in both tyrosine kinase and neurogenic intercellular signaling pathways. Moreover, the functions of brn in oogenesis are distinct from those of Notch and Delta, two other neurogenic loci that are known to be required for follicular development. 相似文献
94.
D Stamatiadis F Dadoun M C Portois F Wright I Mowszowicz P Mauvais-Jarvis 《The Journal of steroid biochemistry and molecular biology》1992,41(1):43-51
Nuclear androgen receptors from cultured genital skin fibroblasts were analyzed by non-denaturing isoelectric focusing (IEF) in ultrathin polyacrylamide gels before and after photoaffinity labeling with [3H]methyltrienolone. Both reversibly and covalently labeled receptors focused at pH 5.28 +/- 0.20 when extracted from nuclei with high salt. Lowering of the salt concentration yielded, in both cases, a second species which focused at pH 7.16. This species became predominant when nuclei were sonicated in IEF sample buffer containing no salt, even after extensive nucleic acid digestion. Low salt cytosols from both prostate and foreskin focused as a single peak of pI: 4.93 +/- 0.31 which remained unchanged when KCl was added to the cytosol up to a concentration of 0.6 M. SDS-polyacrylamide gel electrophoresis of photoaffinity labeled receptors revealed labeled proteins with Mw 90-95 kDa. Two-dimensional electrophoresis of photoaffinity labeled nuclear receptors, extracted in low or high salt, showed that the two isoforms (pI 5.28 and 7.16) contain the same steroid-binding subunit with Mw 90-95 kDa. Nuclear receptors from 4 patients with the receptor positive form of the Complete Androgen Insensitivity Syndrome (CAIS, Rc+) were analyzed by non-denaturing IEF: a single species was observed, focusing at pH 6.0 whether in high or low salt conditions. These results indicate that the nuclear androgen receptor is an acidic protein with pI 5.28 and Mw 90-95 kDa under maximum protein dissociation conditions. When extracted under low salt conditions, it can be isolated in a neutral form (pI 7.16) suggesting its association with a nuclear protein. Receptors of (CAIS, Rc+) patients have an abnormal charge and show no pI shift upon lowering of the salt concentration suggesting that this shift could be a significant step in the mechanism of action of androgens. 相似文献
95.
B A Wright D McFadden 《Philosophical transactions of the Royal Society of London. Series B, Biological sciences》1992,336(1278):325-8; discussion 328-9
Delaying the onset of a signal relative to the onset of a simultaneous notched masker often improves the ability of listeners to 'hear out' the signal at both threshold and suprathreshold levels. Viemeister & Bacon (J. acoust. Soc. Am., 71, 1502-1507 (1982)) suggested that such auditory enhancement effects could be accounted for if the suppression produced by the masker on the signal frequency adapted, thereby releasing the signal from suppression. In support of their hypothesis, Viemeister & Bacon reported that a masker preceded by an enhancer having no component at the signal frequency produced more forward masking than did the masker by itself. Here evidence is provided from five new experiments showing that adaptation of psychophysical two-tone suppression is inadequate to account either for auditory enhancement effects or for the enhanced forward masking demonstrated by Viemeister & Bacon. 相似文献
96.
Cyclic amplification and selection of targets (CASTing) for the myogenin consensus binding site. 总被引:47,自引:18,他引:29 下载免费PDF全文
The consensus binding site for the muscle regulatory factor myogenin was determined from an unbiased set of degenerate oligonucleotides using CASTing (cyclic amplification and selection of targets). Stretches of totally random sequence flanked by polymerase chain reaction priming sequences were mixed with purified myogenin or myotube nuclear extracts, DNA-protein complexes were immunoprecipitated with an antimyogenin antibody, and the DNA was amplified by polymerase chain reaction. Specific binding was obtained after four to six cycles of CASTing. The population of selected binding sites was then cloned, and a consensus was determined from sequencing individual isolates. Starting from a pool with 14 random bases, purified myogenin yielded a consensus binding site of AACAG[T/C]TGTT, while nuclear extracts retrieved the sequence TTGCACCTGTTNNTT from a pool containing 35 random bases. The latter sequence is consistent with that predicted from combining an E12/E47 half-site (N[not T]CAC) with the purified myogenin half-site ([T/C] TGTT). The presence of paired E boxes in many of the sequences isolated following CASTing with nuclear extracts proves that myogenin can bind cooperatively with other E-box-binding factors. 相似文献
97.
Raffaele Del Buono Massimo Pignatelli Walter F. Bodmer Nicholas A. Wright 《Differentiation; research in biological diversity》1991,46(2):97-103
The relationship between the adhesion of five human colorectal carcinoma cell lines to extracellular matrix (ECM) proteins, namely type I collagen, type IV collagen, fibronectin, laminin and basement membrane extract (Matrigel), and the ability of these cells to express morphological differentiation when grown in a basement membrane extract (Matrigel) or on normal rat mesenchymal cells has been examined. Two cell lines, SW1222 and HRA-19, organised into glandular structures, with well-defined polarity when cultured on both substrata as well as in three-dimensional (3D) collagen gel culture as previously shown. The remaining three cell lines (SW620, SW480 and HT29) grew as loose aggregates or as they would normally grow on tissue culture plastic. Addition to the culture medium of a hexapeptide, containing the cell-matrix recognition sequence arginine-glycine-aspartic acid (RGD), inhibited attachment and glandular formation of SW1222 and HRA-19 when these cells were grown on living mesenchymal cells, but not in Matrigel. The morphological differentiation of HRA-19 cells in 3D-collagen was also inhibited by the same RGD-containing peptide, as previously shown for SW1222 cells. Attachment of the remaining three cell lines was inhibited on mesenchyme but not in Matrigel, further supporting the specificity of the peptide effect on epithelial-mesenchymal binding. In conclusion we have shown that colorectal tumour cells are able to bind ECM proteins and that the cellular binding is an essential step in the induction of the morphological differentiation seen on living mesenchymal cells, in basement membrane extracts and in type I collagen gel.(ABSTRACT TRUNCATED AT 250 WORDS) 相似文献
98.
Summary Adult rainbow trout (Oncorhynchus mykiss) were injected intraperitoneally with capsaicin, substance P, serotonin, or a control of saline vehicle or bovine serum albumin (0.5 g/g body weight). Fish were sacrificed 30 min and 1,2 and 4 h post-injection, the gut was dissected out, and a small section of the upper intestine was processed for electron microscopy. A significant proportion of eosinophilic granule cells (EGCs) of the intestine were in close association with non-myelinated neuronal bundles in all fish (4 fish per treatment and time period), but there was no significant difference between treatment or time, suggesting that the association was unaffected by these factors. Close examination of EGC ultrastructure showed that fish treated with capsaicin and substance P exhibited limited degranulation of the EGCs in the stratum compactum and extensive crinophagic-like degranulation in the lamina propria. Cells of the lamina propria contained characteristic multivesicular-like bodies. The degranulation was reminiscent of both mast cell degranulation and endocrine cell crinophagy. EGCs of fish treated with serotonin or a control were unaffected, suggesting that the serotoninergic neurons, believed to be involved in gut motility, were not responsible for degranulation. It is apparent that EGCs of the trout intestine may be under nervous control, as has been demonstrated previously for mammalian mast cells. 相似文献
99.
The molecular mechanism of inhibition of alpha-type DNA polymerases by N2-(butylphenyl)dGTP and 2-(butylanilino)dATP: variation in susceptibility to polymerization. 总被引:2,自引:2,他引:0 下载免费PDF全文
Calf thymus DNA polymerase alpha (pol alpha) and bacteriophage T4 DNA polymerase (pol T4) were exploited as model enzymes to investigate the molecular mechanism of inhibitory action of N2-(p-n-butylphenyl)dGTP (BuPdGTP) and 2-(p-n-butyl-anilino)dATP (BuAdATP) on the BuPdNTP-susceptible alpha polymerase family. Kinetic analysis of inhibition of pol alpha with mixtures of complementary and noncomplementary template:primers indicated that both nucleotides induced the formation of a polymerase: inhibitor:primer-template complex. Primer extension experiments using the guanine form as the model analog indicated that pol alpha cannot utilize these nucleotides to extend primer termini. In contrast, pol T4 polymerized BuPdGTP, indicating that resistance to polymerization is not a common feature of the inhibitor mechanism among the broad membership of the alpha polymerase family. 相似文献
100.