全文获取类型
收费全文 | 128941篇 |
免费 | 6987篇 |
国内免费 | 174篇 |
专业分类
林业 | 5367篇 |
农学 | 3706篇 |
基础科学 | 785篇 |
14291篇 | |
综合类 | 24078篇 |
农作物 | 4839篇 |
水产渔业 | 5751篇 |
畜牧兽医 | 68036篇 |
园艺 | 1579篇 |
植物保护 | 7670篇 |
出版年
2018年 | 1852篇 |
2017年 | 1974篇 |
2016年 | 1737篇 |
2015年 | 1600篇 |
2014年 | 1900篇 |
2013年 | 4852篇 |
2012年 | 3542篇 |
2011年 | 4305篇 |
2010年 | 2816篇 |
2009年 | 2842篇 |
2008年 | 4192篇 |
2007年 | 3985篇 |
2006年 | 3724篇 |
2005年 | 3412篇 |
2004年 | 3271篇 |
2003年 | 3382篇 |
2002年 | 3125篇 |
2001年 | 3746篇 |
2000年 | 3808篇 |
1999年 | 3015篇 |
1998年 | 1233篇 |
1997年 | 1197篇 |
1995年 | 1336篇 |
1994年 | 1174篇 |
1993年 | 1213篇 |
1992年 | 2511篇 |
1991年 | 2846篇 |
1990年 | 2655篇 |
1989年 | 2659篇 |
1988年 | 2415篇 |
1987年 | 2438篇 |
1986年 | 2539篇 |
1985年 | 2511篇 |
1984年 | 1962篇 |
1983年 | 1780篇 |
1982年 | 1191篇 |
1979年 | 1902篇 |
1978年 | 1492篇 |
1977年 | 1361篇 |
1976年 | 1267篇 |
1975年 | 1377篇 |
1974年 | 1751篇 |
1973年 | 1736篇 |
1972年 | 1736篇 |
1971年 | 1607篇 |
1970年 | 1631篇 |
1969年 | 1505篇 |
1968年 | 1355篇 |
1967年 | 1347篇 |
1966年 | 1187篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
111.
112.
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
113.
S. Dänicke I. Halle E. Strobel E. Franke & H. Jeroch 《Journal of animal physiology and animal nutrition》2001,85(9-10):301-313
114.
Six bullmastiffs with congenital heart disease were evaluated over a three-year period. In all the cases the problem was shown to be dysplasia of the pulmonary valve. Five cases were male, one was female. All dogs available to follow-up developed signs of cardiac decompensation. Bullmastiffs must be added to the list of breeds in which valvular pulmonic stenosis is encountered frequently. 相似文献
115.
Mangroves as indicators of coastal change 总被引:2,自引:0,他引:2
In view of the unique biological characteristics of mangroves, it is interesting to assess the extent to which these ecosystems can be used as indicators of coastal change or sea-level rise. From recent studies of mangrove mortality at several locations (including Guiana, Gambia, Côte d'Ivoire, Kenya, India and Bangladesh), it appears that these coastal ecosystems are so specialized that any minor variation in their hydrological or tidal regimes causes noticeable mortality. Each species of mangrove (but particularly those belonging to the genera Rhizophora, Bruguiera, Sonneratia, Heritiera and Nypa) occurs in ecological conditions that approach its limit of tolerance with regard to salinity of the water and soil, as well as the inundation regime. If the duration of daily immersion were to be modified by tectonic, sedimentological or hydrological events, the species either readjusts to the new conditions or succumbs to unsuitable conditions. Consequently, the use of remote sensing data for mangrove ecosystems offers excellent potential as a tool for monitoring coastal change. 相似文献
116.
The effect of exploratory laparotomy on the serum and peritoneal haptoglobin concentrations of the pony. 总被引:1,自引:0,他引:1
下载免费PDF全文
![点击此处可从《Canadian journal of veterinary research》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Serum haptoglobin concentration was used as an indicator of the acute phase response in ponies undergoing exploratory laparotomy. Preoperative, 1 h intraoperative, 3 h, 6 h, 12 h and 24 h postoperative blood samples and 48 h postoperative peritoneal fluid samples were obtained for haptoglobin analysis. A spectrophotometric assay based on cyanmethemoglobin binding capacity (CyanBC) was used to determine haptoglobin concentrations. The preoperative reference range for serum haptoglobin concentrations in these ponies was 25-60 mg CyanBC/dL. Intraoperative and 3 h postoperative blood samples had decreased haptoglobin concentrations when compared to preoperative values. Serum haptoglobin concentrations began to rise by the 6 h postoperative sample and were generally elevated above preoperative values by the 24 h postoperative sample. Two of the ten ponies had mild signs of postoperative colic which were associated with twofold elevations in serum haptoglobin concentrations and fivefold elevations in peritoneal fluid haptoglobin concentrations. 相似文献
117.
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
118.
119.
120.
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