全文获取类型
收费全文 | 9439篇 |
免费 | 766篇 |
专业分类
10205篇 |
出版年
2021年 | 92篇 |
2020年 | 42篇 |
2019年 | 72篇 |
2018年 | 96篇 |
2017年 | 108篇 |
2016年 | 140篇 |
2015年 | 218篇 |
2014年 | 285篇 |
2013年 | 502篇 |
2012年 | 388篇 |
2011年 | 401篇 |
2010年 | 261篇 |
2009年 | 252篇 |
2008年 | 431篇 |
2007年 | 441篇 |
2006年 | 399篇 |
2005年 | 432篇 |
2004年 | 446篇 |
2003年 | 434篇 |
2002年 | 346篇 |
2001年 | 376篇 |
2000年 | 393篇 |
1999年 | 334篇 |
1998年 | 108篇 |
1997年 | 116篇 |
1996年 | 102篇 |
1995年 | 113篇 |
1994年 | 91篇 |
1993年 | 97篇 |
1992年 | 236篇 |
1991年 | 223篇 |
1990年 | 240篇 |
1989年 | 195篇 |
1988年 | 186篇 |
1987年 | 174篇 |
1986年 | 150篇 |
1985年 | 146篇 |
1984年 | 123篇 |
1983年 | 107篇 |
1982年 | 85篇 |
1981年 | 68篇 |
1980年 | 55篇 |
1979年 | 85篇 |
1978年 | 81篇 |
1977年 | 68篇 |
1976年 | 45篇 |
1975年 | 39篇 |
1974年 | 49篇 |
1973年 | 40篇 |
1972年 | 48篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
Shigeo Yamamoto Miki Yokogawa Kyomi Wakamatsu Hiroyuki Kataoka Masami Makita 《Journal of chromatography. B, Analytical technologies in the biomedical and life sciences》1982,233(1):29-38
A gas chromatographic method was developed for the determination of monoacetylputrescine, monoacetylcadaverine, N1-acetylspermidine and N5-acetylspermidine in human urine. The amines were isolated from urine by silica gel column chromatography. 1, 10-Diaminodecane was used as internal standard. The amines were reacted with ethyl chloroformate in aqueous medium to four ethyloxycarbonyl derivatives prior to application to gas chromatography using a flame ionization detector. Separation and determination of the derivatives were carried out on a Uniport HP column (1.0 m) impregnated with 0.5% SP-1000 under temperature-programmed conditions. The monoacetylpolyamines could be measured accurately at the nanomole level. The method was used for the determination of the monoacetylpolyamines in urine of healthy volunteers. The values obtained were in the range of the published data. 相似文献
82.
Unrolling due to blue light (B) irradiation of the second leavesdetached from 8-day-old rice (Oryza saliva L.) seedlings wassimilar to that reported previously for nondetached leaves.The effect of B was counteracted by irradiation with red light(R). The counteracting effect of R was reversed by subsequentirradiation with far-red light (FR). When the detached leaf was irradiated with B passed througha 1-mm-wide slit 5, 8, 10, 12 or 15 mm from the leaf tip, irradiation10 mm from the leaf tip was the most effective. The effect of a 1 mm-wide-B irradiation 10 mm from the leaftip was counteracted by a 1 mm-wide-R irradiation at the sameposition, but not by irradiations at the other points. The counteractingeffect of R was reversed by a 1 mm-wide-FR irradiation at thesame position. This suggests that the excitation or the reactionof the B photoreceptor(s) is affected directly by the PFR formof phytochrome. The dose-response curve for the unrolling caused by B showeda simple Bunsen-Roscoe relation without two peaks, which differsfrom that for the phototropism in Avena caused by B. (Received August 21, 1980; Accepted December 20, 1980) 相似文献
83.
Katsuhiko Tachibana Yoshifumi Yamamoto Etsuro Osaki Yoshikazu Kuroki 《Human genetics》1980,54(2):283-286
Summary A 7-month-old boy with the cerebro-costomandibular syndrome is presented. This is the first case report in an Oriental population.15 reported cases in the literature are reviewed. 相似文献
84.
Yoshikazu Kuroki Ichiro Matsui Yoshifumi Yamamoto Atsushi Ieshima 《Human genetics》1980,55(2):227-229
Summary Disomic and trisomic cells of a patient with Down syndrome mosaic were used to study the effect of the additional chromosome 21 against an identical genetic background. The frequency of Ag staining and the participation in satellite associations were determined for each pair of acrocentric chromosomes. The additional chromosome 21 of the trisomic cells and its homologues proved to be regularly Ag positive. Therefore the trisomic cells showed more Ag positive chromosomes and more satellite associations per cell than the diploid cells. Thus, no compensation for the additional rRNA-gene dose could be found in the cells of the trisomic line. 相似文献
85.
Purification and some properties of beta-lactamases from Proteus rettgeri and Proteus inconstans 总被引:2,自引:0,他引:2
Two beta-lactamases were isolated from strains of Proteus species and purified, one from a strain of P. rettgeri and the other from a strain of P. inconstans. Each enzyme preparation gave a single protein band on polyacrylamide gel electrophoresis. Molecular weights of P. rettgeri and P. inconstans enzymes were found to be 42,000 and 43,000, and their isoelectric points pH 8.7 and 8.6, respectively. The two enzymes presented typical cephalosporinase profiles. Cefmetazole (CS-1170) and cefoxitin, both cephamycin antibiotics, not only resisted hydrolysis by both of the enzymes, but also inhibited their activities competitively. Rabbit antiserum against purified P. rettgeri enzyme inhibited the activity of both purified and crude enzyme preparations from other strains of P. rettgeri so far tested. None of the beta-lactamases produced by other species of Proteus including P. inconstans was inhibited by the antiserum, thus showing that the purified cephalosporinase was of the species-specific types. The enzymological properties of the preparations were compared with those of beta-lactamases derived from other gram-negative enteric bacteria. 相似文献
86.
Regulation or procollagen messenger ribonucleic acid levels in Rous sarcoma virus transformed chick embryo fibroblasts 总被引:19,自引:0,他引:19
Using cloned cDNAs for pro-alpha 1 and pro-alpha 2 collagen messenger ribonucleic acid (mRNA), we have investigated the regulation of collagen mRNA levels in Rous sarcoma virus (RSV) transformed chick embryo fibroblasts (CEF). We find that both pro-alpha 1 and pro-alpha 2 mRNA levels are decreased approximately 10-fold in CEF transformed by either the Bryan high-titer strain or the Schmidt-Ruppin strain of RSV. Using temperature-sensitive mutants in the transforming gene src, we also investigated the rate of change in the levels of the two mRNA species. We employed mutants of both the Bryan high-titre strain (BHTa) and the Schmidt-Ruppin strain (ts68). With both mutants the results were similar. Upon shift from the permissive temperature (35 degrees C) to the non-permissive temperature (41 degrees C), collagen mRNA synthesis, did not increase until more than 5 h had passed, suggesting that action of src on collagen gene expression is indirect. Upon shift from 41 to 35 degrees C, collagen mRNA levels fell with a half-life of 10 h. Whether this fall reflects the half-life of procollagen mRNA or an effect of src on procollagen RNA stability is unclear. Both pro-alpha 1 and pro-alpha 2 mRNA levels were coordinately controlled. 相似文献
87.
Anti-idiotypic antibodies against TEPC-15 myeloma protein (BALB/c origin) were raised in allogeneic animals by immunization of A/J mice with the myeloma protein. The antibody activities were fractionated into two specificities by TEPC-15 immunoadsorbent affinity columns by elution with free hapten (phosphorylcholine, PC), followed by elution with acidic buffer (glycine- HCl, pH 2.3). Idiotype binding analysis indicated that the fraction eluted with hapten could be inhibited in its binding to TEPC-15 by free hapten (i.e., binding site-directed anti-idiotypic antibody), whereas the acid-eluted fraction could not (i.e., framework-directed anti-idiotypic antibody). When analyzed for their biological activities on PC-specific B lymphocytes producing T-15 idiotype-bearing antibodies, both anti-idiotypic antibody fractions had similar suppressive effects on the in vitro production of antiphosphorylcholine antibody in culture. 相似文献
88.
89.
90.