全文获取类型
收费全文 | 6245篇 |
免费 | 354篇 |
国内免费 | 3篇 |
专业分类
6602篇 |
出版年
2022年 | 41篇 |
2021年 | 70篇 |
2020年 | 32篇 |
2019年 | 52篇 |
2018年 | 73篇 |
2017年 | 67篇 |
2016年 | 116篇 |
2015年 | 193篇 |
2014年 | 234篇 |
2013年 | 408篇 |
2012年 | 340篇 |
2011年 | 375篇 |
2010年 | 222篇 |
2009年 | 195篇 |
2008年 | 354篇 |
2007年 | 349篇 |
2006年 | 329篇 |
2005年 | 331篇 |
2004年 | 332篇 |
2003年 | 334篇 |
2002年 | 341篇 |
2001年 | 148篇 |
2000年 | 143篇 |
1999年 | 144篇 |
1998年 | 84篇 |
1997年 | 61篇 |
1996年 | 50篇 |
1995年 | 41篇 |
1994年 | 53篇 |
1993年 | 51篇 |
1992年 | 90篇 |
1991年 | 85篇 |
1990年 | 69篇 |
1989年 | 81篇 |
1988年 | 71篇 |
1987年 | 42篇 |
1986年 | 48篇 |
1985年 | 59篇 |
1984年 | 54篇 |
1983年 | 55篇 |
1982年 | 33篇 |
1981年 | 27篇 |
1980年 | 26篇 |
1979年 | 43篇 |
1978年 | 25篇 |
1977年 | 21篇 |
1976年 | 23篇 |
1975年 | 22篇 |
1973年 | 21篇 |
1965年 | 15篇 |
排序方式: 共有6602条查询结果,搜索用时 15 毫秒
51.
Marcus J. Swann David Bloor Tetsuya Haruyama Masuo Aizawa 《Biosensors & bioelectronics》1997,12(12):13
A fructose dehydrogenase (FDH) modified electrode is produced by the electroadsorption of a layer of FDH on a platinum electrode followed by the electropolymerization of a polypyrrole (PPy) film around and over the enzyme. This immobilizes and stabilizes the enzyme as well as providing an electron transfer pathway to the electrode. The amperometric response to fructose and the enzymatic activity are measured as a function of PPy film thickness. The electrode is shown to have a maximum response at a PPy thickness of approximately the thickness of the enzyme layer. A measure of the electrode efficiency is also obtained, this is the amperometric response to fructose as a percentage of that expected on the basis of the enzyme activity. The functioning of the electrode is also dependent on the counter-ion used for PPy polymerization. This is shown to be mainly related to the nucleation and growth of the PPy film in the interfacial region. 相似文献
52.
53.
Methionine sulfoximine (MSO) greatly reduced the carbon dioxideexchange rate (CER) of detached wheat (Triticum aestivvm L.cv Roland) leaves in 21% O2, but only slightly reduced it in2% O2. A supply of 50 mM NH4Cl had little effect on the CERirrespective of the O2 concentration. A simultaneous additionof glutamine and MSO protected against the inhibition of photosynthesisto a considerable extent and caused the accumulation of moreNH3 than did the addition of MSO alone. Fixation of 14CO2 in wheat leaves was inhibited by MSO treatmentin 22% O2, and there was decreased incorporation of 14G intoamino acids and sugars and increased label into acid fractions.The addition of MSO and glutamine together eliminated the effectof MSO on the photosynthetic 14CO2 fixation pattern. NH4Cl stimulatedthe synthesis of amino acids from 14CO2, especially the synthesisof serine in 22% O2. Our observations show that factors other than the uncouplingof photophosphorylation by accumulated NH3 may be responsiblefor the early stage of photosynthesis inhibition by MSO underphotorespiratory conditions.
1Present address: Department of Agricultural Chemistry, KyushuUniversity, Fukuoka 812 Japan.
2Also at U.S. Department of Agriculture, Agricultural ResearchService, Urbana, Illionois 61801, U.S.A. (Received September 13, 1983; Accepted February 2, 1984) 相似文献
54.
Thyroglobulin-like immunoreactivity of the parafollicular cells was studied by an immunoperoxidase bridge technique using antisera against dog thyroglobulin fragments. 1. The dog parafollicular cells were specifically stained by anti-peak I (27S and larger components fraction) antiserum absorbed with peak II (19S fraction). By this method, they were easily distinguishable from the non-reactive follicular cells and colloid droplets. More sensitive staining of the parafollicular cells was possible with anti-peak I' (larger components fraction) antiserum. The staining reactions indicated that the antigenic material responsible for immunoreactivity of the parafollicular cells was due to larger molecular components of thyroglobulin corresponding to 32S, 37S or greater than 37S, and was not due to either the 19S thyroglobulin or to the 27S iodoprotein. 2. A conspicuous decrease of the immunoreactive material in the parafollicular cells occurred in the dog after both chronically induced hypercalcemia and antithyroid drug treatment. This coincided with movement of secretory granules containing calcitonin as shown by staining with silver impregnation, HCl-basic dye, and lead-hematoxylin. 3. The antisera against larger molecular components of dog thyroglobulin showed a high degree of cross-reactivity to the parafollicular cells of most of the mammalian species investigated; rats, rabbits, hamsters, mice, cats, lions, goats, cows, and human. 相似文献
55.
56.
57.
Hiroshi Ikeda 《Primates; journal of primatology》1982,23(3):338-347
Population changes and home range utilization of the wild Japanese monkey at Mt. Kawaradake have been studied since 1972.
Age compositions of this troop were obtained over a seven-year period. Troop size decreased from over 100 to 40 individuals
as a result of a capture in 1974.
The capture affected directly and indirectly the troop's range and population dynamics. The troop reduced its range size from
4.7 km2 to 2.67 km2 and changed its utilization pattern in relation to the decrease in size. After the capture, the troop used one particular
area intensively, whereas the rhythmic nomadic pattern had been observed as before. This may have been caused by the decrease
in the overall food requirement of the troop.
The birth rate increased significantly after the capture. However, troop size did not increase because of the low recruitment
rate for adult females and the high mortality of juveniles. 相似文献
58.
Pathological and microbiological studies were conducted on lesions in the lungs of 194 calves from mass rearing facilities. Macroscopically, the lesions were classified into six forms: nonlesion, atelectasis, mild pneumonia, moderate pneumonia, advanced pneumonia, and advanced pneumonia accompanied with abscess. Histopathological examination revealed bronchopneumonia in most of the calves. Lesions more advanced than moderate pneumonia were complicated with desquamation, severe exudation, and necrosis. Bacteriologically, Pasteurella sp. was isolated often in combination with Staphylococcus sp. from about a half of the atelectatic cases. With the development of pneumonic lesions, Pasteurella sp. was isolated at a high frequency in combination with Haemophilus sp., Streptococcus sp., and Corynebacterium sp. Prominent necrosis was more often seen in cases with Pasteurella haemolytica isolated than in cases with only Pasteurella multocida isolated. Mycoplasma sp. and Ureaplasma sp. were isolated from distinctly pneumonic lesions. Advanced pneumonic lesions were observed in many calves over 30 days of age. The importance of environmental and managerial improvement was also emphasized, since calf pneumonia tended to break out in facilities under unsatisfactory conditions in the present work. 相似文献
59.
H Takeuchi H Tamura A Kumagai M Ikeda 《Comptes rendus des séances de la Société de biologie et de ses filiales》1979,173(5):980-988
The influences of two water soluble contrast media, meglumine iothalamate and meglumine iocarmate, on the neuronal excitability and on the neuronal sensitivity to putative transmitters were examined in comparison with those of sucrose using two identifiable giant neurones of Achatina fulica Férussac (the TAN and the PON). A relatively low increase of osmotic pressure of the extracellular fluid, produced by the application of contrast media, reversed the Cl- dependent inhibition caused by a putative transmitter. The same increase of this osmotic pressure, however, did not influence the Cl- independent inhibition and the excitation of the neurone examined. The hyperpolarization of neuromembrane was caused by an increase of osmotic pressure of the extracellular fluid. Its relatively high increase was necessary to make spontaneous spike discharges disappear totally. All effects of the two contrast media, observed in this study, were due to the increase of osmotic pressure of the extracellular fluid ; no specific effect of the contrast media containing the iodine on the indicators used was observed. 相似文献
60.
Summary The role of the recA gene product of Escherichia coli in genetic recombination was examined in a system where recombination takes place in the absence of protein synthesis. recA200 bacteria were infected with two mutant strains of phage lambda in the presence of chloramphenicol and rifampin, and the resulting recombinant DNA molecules were measured by in vitro packaging. When recA200 bacteria grown at a temperature that is permissive for RecA phenotype were transferred to a temperature that is restrictive for RecA phenotype in the presence of the inhibitors, recombination of the infecting phages was severely blocked. This result shows that the recombination activity of the recA200 cells is inactivated by the change of temperature even in the absence of protein synthesis. The most likely explanation of this result is that the recA protein is directly involved in the recombination detected in the presence of chloramphenicol and rifampin. 相似文献