全文获取类型
收费全文 | 8598篇 |
免费 | 676篇 |
国内免费 | 610篇 |
出版年
2024年 | 36篇 |
2023年 | 189篇 |
2022年 | 209篇 |
2021年 | 262篇 |
2020年 | 271篇 |
2019年 | 319篇 |
2018年 | 319篇 |
2017年 | 267篇 |
2016年 | 275篇 |
2015年 | 291篇 |
2014年 | 494篇 |
2013年 | 616篇 |
2012年 | 373篇 |
2011年 | 539篇 |
2010年 | 448篇 |
2009年 | 423篇 |
2008年 | 475篇 |
2007年 | 465篇 |
2006年 | 369篇 |
2005年 | 340篇 |
2004年 | 310篇 |
2003年 | 258篇 |
2002年 | 232篇 |
2001年 | 148篇 |
2000年 | 145篇 |
1999年 | 165篇 |
1998年 | 130篇 |
1997年 | 142篇 |
1996年 | 122篇 |
1995年 | 119篇 |
1994年 | 125篇 |
1993年 | 118篇 |
1992年 | 101篇 |
1991年 | 96篇 |
1990年 | 65篇 |
1989年 | 49篇 |
1988年 | 60篇 |
1987年 | 48篇 |
1986年 | 39篇 |
1985年 | 73篇 |
1984年 | 73篇 |
1983年 | 54篇 |
1982年 | 65篇 |
1981年 | 35篇 |
1980年 | 29篇 |
1979年 | 31篇 |
1978年 | 18篇 |
1977年 | 9篇 |
1976年 | 15篇 |
1975年 | 10篇 |
排序方式: 共有9884条查询结果,搜索用时 31 毫秒
81.
The myxobacterium, Corallococcus (Myxococcus) coralloides strain Cc c127, could not utilize mono- and disaccharides, but maltotriose and the polysaccharides starch, amylose, amylopectin, and pullulan stimulated growth. Radioactive CO2 was set free from 14C-labeled starch. When starch was degraded, small amounts of maltose and glucose accumulated in the culture supernatant. Maltotriose, however, appeared only temporarily. Outside the cells, the trisaccharide could not be split into glucose and maltose. Pullulan was hydrolyzed exclusively into a trisaccharide which during growth was immediately consumed. Hexokinase, glucose-6-phosphate dehydrogenase, 6-phosphogluconate dehydrogenase and phosphoglucomutase could readily be demonstrated in cell extracts, but fructose-1,6-diphosphate aldolase was present with low activity only. The data suggest that intracellular glucose is metabolized mainly via the pentose phosphate pathway.Prof. Dr. Gerhard Drews gratefully dedicated to his 60th birthday 相似文献
82.
The performance of The Subhuman Primate Pregnancy Test Kit was evaluated for routine detection of early (days 19-21) pregnancy in the rhesus monkey. Out of 123 confirmed matings, 19 resulted in pregnancy. In the pregnant animals the kit had an accuracy of 73.7%. In the nonpregnant females the accuracy was higher, 88.5%. False positives were encountered in ovariectomized females as well as adult intact males. 相似文献
83.
‘ATG vectors’ for regulated high-level expression of cloned genes in Escherichia coli 总被引:67,自引:0,他引:67
A plasmid cloning vector system has been constructed that allows for the production of large quantities of foreign proteins or fragments thereof, in an unfused state. These vectors provide strong regulated trp-lac fusion promoters and the lacZ ribosome-binding site (RBS) followed by an ATG translation initiation codon at an appropriate distance from the RBS. The ATG codon is located within a unique NcoI restriction site (CCATGG). Digestion with NcoI exposes the ATG for fusion. Gene fragments lacking a prokaryotic RBS and/or ATG start codons can be inserted in several ways. Expression experiments using a truncated cI gene of bacteriophage A or a large portion of the coding region of the Herpes simplex virus type l glycoprotein D gene have been performed. The results of these studies show that the vectors are useful for the high-level expression of prokaryotic and eukaryotic genes in Escherichia coli. 相似文献
84.
Nonrandom insertion of Tn5 into cloned human adenovirus DNA 总被引:4,自引:0,他引:4
85.
Synopsis Laboratory studies were conducted on 15 schools of blackchin shiners, Notropis heterodon, to determine if they altered their structure in response to changing environmental demands. The hypothesis tested was that fish schools should sacrifice a flat, hydrodynamically efficient structure in favour of an unobstructed visual field in the presence of a predator by staggering in the vertical plane. Ten schools were exposed for two weeks to a simple environment with only a current. For the next two-week period a predator was added. Five control schools were exposed to the simple environment for both two-week periods. Six of the ten treated schools increased their staggering in the vertical dimension as predicted while none of the control schools changed. This result was suggestive that hydrodynamic advantages were sacrificed. Respirometer experiments indicated these fish were capable of achieving some hydrodynamic benefits from schooling but these benefits may be a function of fish size. 相似文献
86.
用人肺鳞癌细胞LTEP-78细胞系免疫Blab/c小鼠获得3株抗人肺癌细胞的单克隆抗体杂交瘤系。其中BLTI-01株经六次克隆化培养,体外传代8个月以上。BLTI-01与白细胞抗原及血型抗原基本上无交叉反应;与骨髓细胞无交叉反应;与癌胚抗原和胎甲球蛋白不相关;与肺鳞癌、肺腺癌细胞系及部分其它肿瘤细胞呈阳性反应。 相似文献
87.
An electrophoretic procedure for separating the molecular forms of catechol-O-methyltransferase in cellulose acetate gel is described; the zones of enzyme activity were revealed by autoradiography. The electrophoretic patterns of the enzyme in several tissues and cell lines derived from four different species are presented.This investigation was supported by Grant 500.6/Ric. 70/1981 from the Italian Ministry of Health and by the Italian Ministry of Education. We are grateful to Dr. M. Castagnola for useful advice and help with thin-layer chromatography. 相似文献
88.
近年来,常用未经丙酮固定的、由丁酸和巴豆油激活的B95-8细胞或P3HR-1细胞为靶细胞,检测人血清中EB病毒IgA/MA抗体以早期诊断鼻咽癌,效果良好。但由于B95-8细胞含有多种EB病毒抗原,不能用丙酮固定,需多次离心沉淀,在浮悬状态下检测,技术比较复杂。 相似文献
89.
Summary Striated Ciliary Roots (SCRs), about 3 m long, are attached to the basal bodies of branchial crown ciliated epithelial cells ofOwenia. These SCRs appear to consist of 5–7-nm diameter filaments organized in a cross-striation pattern with an apparent variable periodicity of 50 to 80 nm. The most exciting observation emerging from this study is the constant and conspicuous close spatial relationship between SCRs and fairly well developed Golgi apparatus. By enhancing contrast and preservation of cell components, the OsFeCN postfixation-staining of material prefixed in glutaraldehyde in the presence of calcium has revealed some fine-structural details within the SCR-Golgi Association. By means of the calcium precipitation method, with antimonate or oxalate in conjunction with X-ray microanalysis, we have identified calcium within SCR dark bands and SCR-associated Golgi bodies. The ability to bind calcium makes the Golgi apparatus a likely candidate for Ca2+ regulation of putative contraction of the SCRs and/or ciliary motility. The slight period variability measured in the SCRs and cytochemical localization of Mg2+, Ca2+-dependent ATPase activities associated with cross striations support the view that theOwenia SCRs may be contractile organelles.The striking and specific close structural association between the Golgi apparatus and the SCR showing Ca2+-binding capabilities suggests that some sort of Ca2+-mediated functional relationship between these organelles may exist.Abbreviations SCR
striated ciliary root
- OsFeCN method
osmium tetroxide-ferricyanide method
- EDTA
ethylenediamine tetraacetic acid
- EGTA
ethyleneglycol-bis-(-aminoethyl ether) N,N-tetraacetic acid
- ATP
adenosine 5-triphosphoric acid
- ATPase
adenosine triphosphatase
- ASW
artificial sea-water 相似文献
90.
Breeding vervet monkeys in a closed environment 总被引:1,自引:0,他引:1
J V Seier 《Journal of medical primatology》1986,15(5):339-349
A breeding group of vervet monkeys produced 95 offspring over five years. Fetal wastage for 114 pregnancies was 16.7%. Uterine sizes were recorded for 103 pregnancies in various stages of gestation. This enabled diagnosis of pregnancy, estimation of stage of gestation, and prediction of parturition to within two weeks. Detailed observations were made on dental eruption, pelage development, and growth of 57 infants. 相似文献