全文获取类型
收费全文 | 63095篇 |
免费 | 3563篇 |
国内免费 | 37篇 |
专业分类
林业 | 2544篇 |
农学 | 1898篇 |
基础科学 | 312篇 |
6909篇 | |
综合类 | 10681篇 |
农作物 | 2166篇 |
水产渔业 | 2880篇 |
畜牧兽医 | 34704篇 |
园艺 | 752篇 |
植物保护 | 3849篇 |
出版年
2018年 | 937篇 |
2017年 | 950篇 |
2016年 | 844篇 |
2015年 | 811篇 |
2014年 | 890篇 |
2013年 | 2681篇 |
2012年 | 1776篇 |
2011年 | 2141篇 |
2010年 | 1329篇 |
2009年 | 1302篇 |
2008年 | 1993篇 |
2007年 | 1952篇 |
2006年 | 1815篇 |
2005年 | 1678篇 |
2004年 | 1598篇 |
2003年 | 1645篇 |
2002年 | 1573篇 |
2001年 | 1868篇 |
2000年 | 1849篇 |
1999年 | 1517篇 |
1998年 | 649篇 |
1997年 | 625篇 |
1996年 | 563篇 |
1995年 | 664篇 |
1994年 | 616篇 |
1993年 | 584篇 |
1992年 | 1282篇 |
1991年 | 1435篇 |
1990年 | 1319篇 |
1989年 | 1321篇 |
1988年 | 1219篇 |
1987年 | 1188篇 |
1986年 | 1243篇 |
1985年 | 1246篇 |
1984年 | 998篇 |
1983年 | 934篇 |
1982年 | 607篇 |
1979年 | 927篇 |
1978年 | 735篇 |
1977年 | 719篇 |
1976年 | 735篇 |
1975年 | 734篇 |
1974年 | 907篇 |
1973年 | 877篇 |
1972年 | 847篇 |
1971年 | 761篇 |
1970年 | 800篇 |
1969年 | 782篇 |
1968年 | 660篇 |
1967年 | 674篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
11.
We compared the results of the ACTH stimulation tests with measurements of alkaline phosphatase and serum cholesterol during Lysodren therapy in 23 dogs with pituitary-dependent hyperadrenocorticism. The ACTH stimulation test proved to be a very sensitive parameter, by which the extent of Lysodren under- or overdosage could be reliably estimated. On the other hand, regulation of the individual Lysodren requirement was not possible by measuring AP and serum cholesterol only. However, it is highly probable that those two parameters can be used to evaluate the general state of metabolism, and they appear to be of prognostic value when greatly elevated. 相似文献
12.
Muscle biopsies were taken from the middle gluteal muscle of 28 Standardbred trotters, 3-4 years of age. The 13 horses in Group T were trained consistently from 18 months of age, whereas the 15 horses in Group UT were not exposed to any systematic training before 3 years of age. Group T horses had a lower percentage of Type IIB fibres (31%) than did Group UT horses (39%). Citrate synthase (CS) activity, representing oxidative capacity, was higher in Group T (72 mmol kg-1 min-1) than in Group UT (47 mmol kg-1 min-1). Biopsies were taken from 4 horses in each group when they were foals and then annually until 3-4 years of age. Results from this study indicate that regular training of Standardbreds from 18 months of age resulted in increased CS activity and a decrease in the percentage of Type IIB fibres. This study shows that training, not growth, is the main factor that induces a high oxidative capacity and a high Type IIA/IIB fibre ratio in muscle of Standardbred trotters. 相似文献
13.
Ovine-derived fibroblasts were used to validate an insulin-like growth factor I (IGF-I) membrane-receptor binding assay system. Competitive binding using fibroblasts revealed that half-maximal inhibition of 125I-IGF-I binding by IGF-I was 2.3 nM. SDS-polyacrylamide gel electrophoresis analysis of specific protein-associated 125I-IGF-I was consistent with the migration of 125I-IGF-I-labeled Type I IGF receptor alpha-subunits at Mr 133,000 daltons. Further, the efficiency of two cell solubilization methods was examined and time-dependent binding equilibrium was determined for the membrane assay system. Satellite cell-derived myotubes were subsequently isolated from primary satellite cell cultures established from the semimembranosus muscles of high and low efficiency-of-gain (EOG) Targhee rams, and IGF-I receptor dynamics were measured. A membrane competitive binding study revealed that half-maximal inhibition of 125I-IGF-I binding was achieved by 1-ng IGF-I for low, and 10-ng IGF-I for high, EOG myotube membrane preparations. Kd values were similar between the high EOG (4.78 nM) and low EOG (2.95 nM) groups; however, receptor concentrations (Bmax) appeared to differ between groups. High EOG membrane receptor Bmax was 3.88 pmole/micrograms protein (19.87 pmole/micrograms DNA), whereas low EOG membrane receptor Bmax was 1.22 pmole/micrograms protein (9.28 pmole/micrograms DNA). These preliminary findings support the hypothesis that genetic selection for EOG results in altered satellite cell responsiveness to IGF-I. 相似文献
14.
J Jieyuan P B Spradbrow 《Zentralblatt für Veterin?rmedizin. Reihe B. Journal of veterinary medicine. Series B》1992,39(5):388-390
Chickens were given various fowlpox vaccines on food pellets--a commercial vaccine (strain M), and the same strain after a single passage on chorio-allantoic membrane or in chicken embryo fibroblasts. All three oral vaccines induced antibodies at levels similar to those induced by commercial strain M administered to the wingweb. The oral vaccine derived from chorio-allantoic membrane gave protection similar to that obtained with vaccine administered by the wingweb, but this required a thousandfold more virus. 相似文献
15.
16.
17.
In this clinical study, a diaphragmatic peritoneo-pericardial hernia in an eight month-old Persian cat is reported. The diagnostic procedure is described, and the clinical symptoms and diagnostic possibilities are discussed. 相似文献
18.
The effect of salinity on seed germination, plant yield parameters, and plant Na, Cl and K concentrations of chickpea and lentil varieties was studied. Results showed that in both crops percentage emergence was significantly reduced by increasing NaCl levels (0–8dSm?1). From the plant growth studies it was found that differences existed among chickpea and lentil varieties in their response to NaCl application. In chickpea, the variety Mariye showed the comparatively lowest germination percentage and the lowest seedling shoot dry weight in response to salinity and was also among the two varieties which had the lowest relative plant height, shoot and root dry weight and grain yield at maturity. Similarly, variety DZ-10-16-2, which was the second best in germination percentage and the highest in terms of seedling shoot dry weight, also had the highest relative plant height, shoot and root dry weights, and grain yield at maturity. In lentil, however, such relationships were less pronounced. Chloride concentration (mg g?1) in the plant parts at salt levels other than the control was about 2–5 times that of Na. K concentration in the plants was significantly reduced by increasing NaCl levels. Chickpea was generally more sensitive to NaCl salinity than lentil. While no seeds were produced at salinity levels beyond 2dSm?1 in chickpea (no seeds were produced at this salt level in the most sensitive variety, Mariye), most lentil varieties could produce some seeds up to the highest level of NaCl application. Overall, varieties R-186 (lentil) and Mariye (chickpea) were the most sensitive of all varieties. On the other hand, lentil variety NEL-2704 and chickpea variety DZ-10-16-2 gave comparatively higher mean relative shoot and root dry weights, and grain yield, thus showing some degree of superiority over the others. The observed variations among the varieties may be useful indications for screening varieties of both crops for salt tolerance. 相似文献
19.
20.
Abstract. Information on land resources and the capacity of land to support agricultural production is a prerequisite for the formation of sound agricultural policies. This paper summarizes Canadian experiences in developing national and regional land evaluation systems. Potential users expected the system to estimate the degree to which changes in biophysical and socio-economic conditions would alter options for land use and production, and to provide a context for more detailed analysis.
A broad-scale land evaluation system was designed to serve the needs identified by representative user groups. Two prototype systems were developed from available information to test the major features of the system design. Neither prototype was complete; one was national in extent and capable of addressing issues of national and provincial importance, the other covered a sub-provincial area but allowed for more detailed evaluation of the effects of soil modifying processes. A full range of applications was demonstrated using one or other of the prototype systems. As a result of this project, the broad-scale land evaluation system design was improved and verified, ongoing research and data collection activities were adjusted to ensure that they meet the needs of a macroscale land evaluation system, and approaches were developed to overcome problems of land evaluation system development. 相似文献
A broad-scale land evaluation system was designed to serve the needs identified by representative user groups. Two prototype systems were developed from available information to test the major features of the system design. Neither prototype was complete; one was national in extent and capable of addressing issues of national and provincial importance, the other covered a sub-provincial area but allowed for more detailed evaluation of the effects of soil modifying processes. A full range of applications was demonstrated using one or other of the prototype systems. As a result of this project, the broad-scale land evaluation system design was improved and verified, ongoing research and data collection activities were adjusted to ensure that they meet the needs of a macroscale land evaluation system, and approaches were developed to overcome problems of land evaluation system development. 相似文献