全文获取类型
收费全文 | 15640篇 |
免费 | 1180篇 |
国内免费 | 1986篇 |
出版年
2023年 | 221篇 |
2022年 | 301篇 |
2021年 | 363篇 |
2020年 | 465篇 |
2019年 | 618篇 |
2018年 | 500篇 |
2017年 | 427篇 |
2016年 | 474篇 |
2015年 | 445篇 |
2014年 | 810篇 |
2013年 | 1091篇 |
2012年 | 654篇 |
2011年 | 640篇 |
2010年 | 554篇 |
2009年 | 658篇 |
2008年 | 695篇 |
2007年 | 820篇 |
2006年 | 777篇 |
2005年 | 670篇 |
2004年 | 603篇 |
2003年 | 586篇 |
2002年 | 583篇 |
2001年 | 491篇 |
2000年 | 372篇 |
1999年 | 369篇 |
1998年 | 336篇 |
1997年 | 293篇 |
1996年 | 289篇 |
1995年 | 301篇 |
1994年 | 269篇 |
1993年 | 239篇 |
1992年 | 264篇 |
1991年 | 304篇 |
1990年 | 230篇 |
1989年 | 176篇 |
1988年 | 198篇 |
1987年 | 152篇 |
1986年 | 165篇 |
1985年 | 186篇 |
1984年 | 155篇 |
1983年 | 108篇 |
1982年 | 170篇 |
1981年 | 148篇 |
1980年 | 148篇 |
1979年 | 98篇 |
1978年 | 85篇 |
1977年 | 63篇 |
1976年 | 55篇 |
1974年 | 36篇 |
1973年 | 43篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
82.
Eimeria tenella: Vitamin Requirements for Development in Primary Cultures of Chicken Kidney Cells 总被引:1,自引:0,他引:1
SYNOPSIS. Development of Eimeria tenella was studied in primary cultures of chicken kidney cells maintained in Medium 199 lacking each of the following: vitamin A. biotin, p -aminobenzoic acid, folic acid, nicotinamide, Ca pantothenate, pyridoxine, pyridoxal, riboflavin, thiamin, ascorbic acid, calciferol, α-tocopherol, and menadione. Data obtained concerning numbers of mature schizonts or total numbers of parasites or both indicated that all of the vitamins are needed for 1st- and 2nd-generation schizogony, and all except calciferol and folic acid are needed for gametogony. 相似文献
83.
SYNOPSIS. Rats inoculated with 10,000 sporulated oocysts of Eimeria nieschulzi had significantly higher total leukocyte counts on postinoculation days (PI) 1, 5, 6 and 7 when compared to control rats. Relative and absolute neutrophil counts increased concomitantly with a decrease in the relative lymphocyte levels in E. nieschulzi-infected rats on PI day 7. Absolute and relative neutrophil counts in infected rats on PI days 7 and 8 were closely correlated with the host's total oocyst discharge. The E. nieschulzi infection had no significant effect on the relative or absolute levels of monocytes or eosinophils. The described changes in leukocyte levels were not paralleled by a significant change in the erythrocyte count. 相似文献
84.
85.
Fluctuation of algal alkaline phosphatase activity and the possible mechanisms of hydrolysis of dissolved organic phosphorus in Lake Barato 总被引:3,自引:3,他引:0
Shuji Hino 《Hydrobiologia》1988,157(1):77-84
For freshwater cyanobacteria, the autofluorescence of phycocyanin is quite high while the in vivo fluorescence (IVF) yield of chlorophyll-a is relatively low, apparently because of low chlorophyll concentrations associated with photosystem II. In eucaryotic phytoplankton, even those with phycobili-protein accessory pigments (e.g. some cryptophytes), the opposite is true. Thus, an IVF ratio which relates phycocyanin to chlorophyll-a signals could be a good index of relative cyanobacterial abundance in the field. Spectrofluorometric scans of whole cells from laboratory cultures indicated that the ratio Em660 @ Ex630/Em680 @ Ex430 could be a very sensitive cyanobacterial indicator. Tandem flowthrough fluorometers were then fitted with the appropriate interference filters and their discriminatory power was evaluated with mixtures of cyanobacterial and eucaryotic phytoplankton. Although subject to many of the constraints of other IVF assays, tandem fluorometry should be particularly appropriate for real-time mapping of the relative spatial and temporal distributions of broad phytoplankton taxa in continuous vertical of horizontal profiles in lakes. 相似文献
86.
S Nozawa S Narisawa R Iizuka T Fukasawa T Kohji P K Nakane K Hirano J L Millan 《Cell biochemistry and function》1989,7(3):227-232
The mechanism of placental alkaline phosphatase (PLAP) induction by prednisolone in a uterine cervical epidermoid cancer cell line SKG-IIIa was investigated in vitro by enzyme-cytochemistry, enzyme immunoassay, Northern and Southern blot analysis, and in situ hybridization. Enzyme-cytochemical alkaline phosphatase (ALP) staining and immunoassay revealed increased levels of PLAP (heat-stable ALP) in prednisolone-treated cells. Northern blot analysis and in situ hybridization showed increased amounts of PLAP mRNA. Southern blot analysis indicated that PLAP was not a product of an amplified or rearranged gene. These findings suggest that the induction of PLAP mRNA in SKG-IIIa cells by prednisolone in turn increased the levels of PLAP. 相似文献
87.
Yu. L. Khmelnitsky A. V. Levashov N. L. Klyachko Karel Martinek 《Enzyme and microbial technology》1988,10(12):710-724
The use of organic media in biocatalysis stems from the fact that in many cases biocatalytic processes can hardly be conducted (if at all) in aqueous solutions because of extremely low solubilities of substrates and/or unfavorable shift of the reaction equilibrium in water. The growing interest in this biotechnological area that has sprung up over the past few years has resulted in various approaches to enzyme stabilization against organic solvents. Thus, the main goal of the present review is to formulate a comprehensive classification of numerous successful nonaqueous biocatalytic systems based on a few fundamental principles. Typical examples are considered, along with the advantages and drawbacks inherent in each of the approaches discussed. 相似文献
88.
S. Kropf 《Biometrical journal. Biometrische Zeitschrift》1988,30(4):461-470
The positive ascertainment of location differences in a multivariate comparison of two or more groups gives rise to the question for the contribution of the single variables or of subsets of variables to the multivariate difference. In this paper two methods are proposed to accomplish the original multivariate test by tests in variable subsets or in single variables using a closed test procedure and Holm's procedure, respectively. Both control the multiple level of the whole procedure. 相似文献
89.
90.
SYNOPSIS. Eimeria dispersa (turkey strain) and Eimeria gallopavonis sporozoites were inoculated into primary cultures of chicken kidney (CK) and turkey kidney (TK) cells. Eimeria dispersa sporozoites were more infective in either cell type than those of E. gallopavonis : at 4 hr, the percentage of infection was 67-98 for E. dispersa but only 23-56 for E. gallopavonis . E. dispersa also survived better in culture: at 2 days, losses of E. dispersa in both cell types were only 4-19%, whereas losses of E. gallopavonis were 35-47% in TK cells and 60–95% in CK cells. However, E. gallopavonis developed further than E. dispersa . Location and increase in numbers of intracellular stages at 4 days indicated that E. dispersa proceeded through 2 schizogonic generations before development stopped. 相似文献