全文获取类型
收费全文 | 14996篇 |
免费 | 1462篇 |
国内免费 | 5篇 |
出版年
2023年 | 56篇 |
2022年 | 196篇 |
2021年 | 357篇 |
2020年 | 195篇 |
2019年 | 246篇 |
2018年 | 313篇 |
2017年 | 260篇 |
2016年 | 447篇 |
2015年 | 776篇 |
2014年 | 788篇 |
2013年 | 903篇 |
2012年 | 1202篇 |
2011年 | 1157篇 |
2010年 | 712篇 |
2009年 | 625篇 |
2008年 | 876篇 |
2007年 | 856篇 |
2006年 | 840篇 |
2005年 | 751篇 |
2004年 | 708篇 |
2003年 | 695篇 |
2002年 | 597篇 |
2001年 | 125篇 |
2000年 | 73篇 |
1999年 | 139篇 |
1998年 | 204篇 |
1997年 | 120篇 |
1996年 | 119篇 |
1995年 | 113篇 |
1994年 | 98篇 |
1993年 | 117篇 |
1992年 | 98篇 |
1991年 | 80篇 |
1990年 | 82篇 |
1989年 | 72篇 |
1988年 | 81篇 |
1987年 | 63篇 |
1986年 | 60篇 |
1985年 | 65篇 |
1984年 | 81篇 |
1983年 | 80篇 |
1982年 | 71篇 |
1981年 | 67篇 |
1980年 | 74篇 |
1979年 | 53篇 |
1978年 | 51篇 |
1976年 | 50篇 |
1975年 | 47篇 |
1974年 | 65篇 |
1973年 | 52篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
PMS was injected thrice weekly for four weeks into first winter and second winter canaries during the following periods: September-October, November-December, January-February and February-March. Measures were made of ovary and oviduct weight, brood-patch development (defeathering, vascularity and sensitivity changes), nest-building and egg-laying. PMS caused overy growth in all months: this was greatest in the second year birds in February. Both control and treated ovaries increased in size towards the breeding season. Oviduct growth depends mainly on the size of the treated ovary. Defeathering was produced by PMS in all months: its rate and extent increased towards the breeding season. Vascularity was also produced by PMS. It was least in November-December but after that the rate at which it appeared increased towards the breeding season. By contrast, the effect of PMS on brood-patch skin sensitivity was greater in the autumn group than subsequently. Nest-building occurred in September-October, but was then very slight until February-March, which is the beginning of the breeding season. Eggs were laid in most months; fewer injections were needed to produce egg-laying as the breeding season approached. 相似文献
102.
103.
Elizabeth G. Cutter 《American journal of botany》1964,51(3):318-324
Regular sequences of leaf and bud formation occur in several members of the Hydrocharitaceae, including Hydrocharis, in which buds are normally formed in the axil of every second leaf of the phyllotactic spiral. Leaf inception begins by periclinal divisions of the inner cells of the 2-layered tunica. Bud formation, which occurs in the apical meristem itself, immediately following the inception of the subtending leaf primordium, begins by divisions in various planes in the corpus, the 2 tunica layers remaining continuous throughout. The young bud meristem soon gives rise to a lateral bud, before leaf formation begins upon it. Because of these and other features, this species is one of considerable morphogenetic interest. Morphogenesis of the whole plant, and in particular the factors controlling the regular sequence of leaf and bud formation, have been and are being investigated experimentally. 相似文献
104.
An Electron Microscope Study of Intranuclear Inclusions in Mouse Liver and Hepatoma 总被引:8,自引:0,他引:8
下载免费PDF全文
![点击此处可从《The Journal of cell biology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
An electron microscope study of intranuclear inclusions which occur in giant cells in a transplantable mouse hepatoma and in enlarged liver cells in mice fed a diet containing bentonite demonstrates that these inclusions are formed by invaginations of the nuclear envelope, and corroborates a previous histochemical study which revealed that the contents of the inclusions are of cytoplasmic origin. In the hepatoma cells the intranuclear inclusions are abundant, small, and situated close to the border of the nucleus, and there are wide openings from the cytoplasm into the invaginations whose contents include lipid droplets, ergastoplasm, and structurally normal mitochondria. In the enlarged liver cells the inclusions are fewer in number, generally much larger than those in the hepatoma, hence they extend deeper into the nucleus, and the interior is continuous with the cytoplasm through only a small opening. Some normal ergastoplasm is present within the inclusions but all other constituents are abnormal. Both normal and degenerating mitochondria occur in the cytoplasm but only degenerating ones are found within the inclusions. Both types of inclusions arise in greatly enlarged cells in which an attempt is made to maintain the normal nuclear surface/nuclear volume ratio by the development of the invaginations of the nuclear envelope. 相似文献
105.
106.
Vanillic, syringic, gallic, and protocatechuic acids, methyl-p-hydroxybenzoate, and propyl-p-hydroxybenzoate generally inhibited respiration in vitro of Escherichia coli, Proteus vulgaris, Pseudomonas aeruginosa, and Aerobacter aerogenes in human urine. In the absence of any other available carbon source, certain of the phenolic compounds were utilized. Reproduction was generally suppressed in urine buffered to pH 7, 5.6, 4.5, and 4.0. The phenolic compounds were used in the range of 0.11 to 0.99 μmole/ml. 相似文献
107.
Cultures of gram-negative bacteria with oxidative glucose metabolism were isolated from surface waters by a highly selective technique, and were classified into 11 types. The predominant type, making up about 50% of the isolated cultures, was cytochrome oxidase-positive, produced fluorescent pigment, and failed to grow at 37 C. A similar type, which differed in being cytochrome oxidase-negative, constituted about 10% of the isolates. Both types of bacteria probably were composed of more than one species. A third type, composed of purple-pigmented pseudomonads, made up approximately 30% of the isolated cultures, and probably represented the predominant species. Other bacterial types isolated constituted less than 10% of the cultures examined. 相似文献
108.
Peter R. Galbraith 《CMAJ》1967,96(25):1636-1641
The mechanism of action of splenic irradiation in the induction of a remission in chronic myelogenous leukemia was investigated in six patients using a leukocyte kinetic approach. The leukocytes were labelled in vitro with radioactive diisopropylfluorophosphate-32 and returned to the circulation. The effect of treatment on the rate of change of leukocyte specific activity was determined. The results suggest (1) that irradiation of the spleen damages granulopoietic cells as they cycle back and forth between the spleen, blood and other extravascular compartments; (2) that damage to exchangeable granulopoietic cells in transit through the irradiated spleen may explain the long remission often encountered after this form of therapy. 相似文献
109.
110.
The linkage between the polysaccharide and mucopeptide components of the cell wall of Lactobacillus casei 总被引:14,自引:8,他引:6
下载免费PDF全文
![点击此处可从《The Biochemical journal》网站下载免费的PDF全文](/ch/ext_images/free.gif)
1. The linkage between the polysaccharide and mucopeptide components of the cell wall of Lactobacillus casei is rapidly hydrolysed under mild acid-hydrolysis conditions. 2. The release of the polysaccharide is accompanied by the hydrolysis of an N-acetylhexosaminide linkage. The N-acetylhexosamine residue readily forms chromogen and it is concluded that it is substituted on C(3) by the adjacent sugar. 3. Continued heating of the polysaccharide in acid results in a slower release of reactive N-acetylhexosamine due to the hydrolysis of glycosidic linkages within the polysaccharide. 4. After the linkage between the polysaccharide and mucopeptide has been hydrolysed, acid phosphatase will release approx. 40% of the total phosphorus as inorganic phosphate. 5. It is concluded that the polysaccharide component of the cell wall is joined through its reducing end group to a phosphate grouping in the mucopeptide. 相似文献