全文获取类型
收费全文 | 55007篇 |
免费 | 3877篇 |
国内免费 | 137篇 |
专业分类
59021篇 |
出版年
2021年 | 403篇 |
2020年 | 371篇 |
2019年 | 396篇 |
2018年 | 853篇 |
2017年 | 821篇 |
2016年 | 1261篇 |
2015年 | 1947篇 |
2014年 | 2128篇 |
2013年 | 2710篇 |
2012年 | 3311篇 |
2011年 | 3132篇 |
2010年 | 1921篇 |
2009年 | 1520篇 |
2008年 | 2580篇 |
2007年 | 2596篇 |
2006年 | 2537篇 |
2005年 | 2401篇 |
2004年 | 2349篇 |
2003年 | 2182篇 |
2002年 | 2199篇 |
2001年 | 1588篇 |
2000年 | 1675篇 |
1999年 | 1348篇 |
1998年 | 561篇 |
1997年 | 441篇 |
1996年 | 424篇 |
1995年 | 403篇 |
1994年 | 421篇 |
1993年 | 379篇 |
1992年 | 825篇 |
1991年 | 803篇 |
1990年 | 764篇 |
1989年 | 724篇 |
1988年 | 674篇 |
1987年 | 597篇 |
1986年 | 589篇 |
1985年 | 549篇 |
1984年 | 495篇 |
1983年 | 457篇 |
1982年 | 410篇 |
1981年 | 404篇 |
1979年 | 503篇 |
1978年 | 378篇 |
1977年 | 326篇 |
1975年 | 382篇 |
1974年 | 360篇 |
1973年 | 341篇 |
1972年 | 364篇 |
1971年 | 329篇 |
1968年 | 314篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
151.
Micronuclei in human lymphocytes irradiated in vitro or in vivo 总被引:1,自引:0,他引:1
Venous blood from healthy donors or from patients with various lympho- and myeloproliferative diseases was incubated in vitro in the presence of cytochalasin B for the induction of binucleated lymphocytes. The time at which cytochalasin B was added depended on the proliferation rate of the lymphocytes. Proliferation was monitored using a semiautomatic microscope photometer/computer system. The background level of micronuclei in binucleated lymphocytes of the patients before radiotherapy was statistically indistinguishable from that of healthy persons. Blood from both groups was irradiated in vitro for the study of the dose-response relationship. The dose-response curves were very similar up to 3.75 Gy, and a somewhat lower micronucleus frequency was found in lymphocytes of patients after a 5-Gy exposure. These in vitro results were compared with in vivo exposure after total-body irradiation of leukemic patients. Due to heavy medication that accompanied radiation therapy, only two doses (1.25 and 2.5 Gy) could be checked after in vivo exposure. There was no statistically significant difference between in vitro and in vivo results after 1.25 Gy, but a slightly lower number of micronuclei was observed after in vivo exposure to 2.5 Gy. 相似文献
152.
153.
154.
Bernd Günzel Sems Yonsel Wolf-Dieter Deckwer 《Applied microbiology and biotechnology》1991,36(3):289-294
Summary The conversion of glycerol to 1,3-propanediol (PD) by Clostridium butyricum DSM 5431 was studied in anaerobic culture. Growth and product formation were optimal at pH = 7.0 and T = 35° C, while aeration rate and stirrer speed were found to have no significant influence. As increasing amounts of initial glycerol led to inhibition of growth, cultivations were done in fed-batch operation. Comparative cultivations were carried out in an air-lift (ALR) and a stirred-tank reactor (STR) having equal working volumes (V
L = 30 l) and no difference in product formation was found. The process was scaled up to reactor sizes of 1.2 m3 (ALR) and 2.0 m3 (STR). The same results were obtained irrespective of reactor volume as well as reactor type (STR/ALR). PD concentrations of approximately 50–58 g·l–1 and overall productivities of 2.3–2.9 g·l–1 ·h–1 could be reached.
Offprint requests to: W.-D. Deckwer 相似文献
155.
W H Schunck F Vogel B Gross E K?rgel S Mauersberger K K?pke C Gengnagel H G Müller 《European journal of cell biology》1991,55(2):336-345
cDNAs were cloned, sequenced and expressed which encode two different cytochrome P-450 forms of the alkane-assimilating yeast Candida maltosa, designated as P-450Cm1 and P-450Cm2. The amino acid sequences deduced were about 55% identical. Expression in Saccharomyces cerevisiae resulted in the formation of intact microsomal P-450 systems catalyzing the hydroxylation of n-hexadecane and lauric acid with significantly different substrate preferences. A massive proliferation of the endoplasmic reticulum was observed in the S. cerevisiae cells which produced P-450. Depending on the P-450 form expressed, distinctly organized stacks of paired membranes appeared and occupied considerable areas of the cytoplasm. As shown by immunoelectron microscopy for P-450Cm1, the protein expressed was highly concentrated within these newly formed membrane structures. 相似文献
156.
Katrin Kausch Clemens R. Müller Tiemo Grimm Kenneth Ricker Marcella Rietschel Sabine Rudnik-Schöneborn Klaus Zerres 《Human genetics》1991,86(3):317-318
Summary Two recent articles have reported the linkage of a gene for recessive spinal muscular atrophy (SMA) on the chromosome region 5q11.2–13.3. Our data show no linkage of the dominantly inherited forms of SMA to this chromosome region. 相似文献
157.
A small deletion and an adjacent base exchange in a potential stem-loop region of the neurofibromatosis 1 gene 总被引:2,自引:2,他引:0
Summary A single-strand conformational polymorphism found in the DNA of a patient with neurofibromatosis 1 (NF1) was shown to be caused by a deletion of a CCACC or CACCT sequence and an adjacent transversion, located about 500 base pairs downstream from the region that codes for a functional domain of the NF1 gene product. This mutation could also be detected in the patient and in his affected daughter by heteroduplex analysis. The deletion removes the proximal half of a small potential stem-loop and interrupts the reading frame in exon 1. A severely truncated protein with a grossly altered carboxy terminus lacking one third of its sequence is expected to be formed from the mutant allele. 相似文献
158.
Cytogenetic and molecular characterization of a newly established neuroblastoma cell line LS 总被引:2,自引:0,他引:2
Günter Rudolph Karin Schilbach-Stückle Rupert Handgretinger Peter Kaiser Horst Hameister 《Human genetics》1991,86(6):562-566
Summary A new human neuroblastoma cell line (LS) that originated from an abdominal tumor of a 16-month-old girl is presented; it was classified, according to Evans, as being stage III. Morphological (dense-core particles) and biochemical characteristics (dopamine--hydroxylase, acetylcholinesterase, neuron-specific-enolase) confirmed the diagnosis. In addition to a slightly variable modal chromosome number of 48 or 49 (because of marker-chromosomes and autosomal trisomies), cytogenetic analysis revealed two constantly appearing chromosomes with homogeneously stained regions (HSR's). The karyo-type remained constant over 50 passages in vitro [49,XX, –12,+der5, + 17,+mar1,+mar2]. Double minutes were a rare phenomenon and appeared only in a few metaphases. In situ hybridization showed that some of the HSR's consisted of amplified N-myc copies. The distribution of the N-myc copies according to in situ hybridization signals along the HSR's was compared with the data of Southern and Northern blotting analyses. 相似文献
159.
160.
Sequence-specific assignments are presented for the polypeptide backbone protons and a majority of the amino-acid-side-chain protons of alpha-neurotoxin from Dendroaspis polylepis polylepis, and individual amide proton-exchange rates with the solvent are reported. The secondary structure and the hydrogen-bonding patterns in the regular secondary structure elements are deduced from nuclear Overhauser effects and the sequence locations of the slowly exchanging amide protons. The molecule includes a three-stranded antiparallel beta-sheet, and there are indications that two additional short chain segments are arranged in an antiparallel beta-sheet. These structural elements are similar, but not identical, to either the secondary structure reported for erabutoxin b in single crystals, or the solution structure of cytotoxin CTXIIb from Naja mossambica mossambica. 相似文献