全文获取类型
收费全文 | 67876篇 |
免费 | 3303篇 |
国内免费 | 367篇 |
专业分类
林业 | 3011篇 |
农学 | 2328篇 |
基础科学 | 710篇 |
7177篇 | |
综合类 | 15787篇 |
农作物 | 2695篇 |
水产渔业 | 2689篇 |
畜牧兽医 | 32507篇 |
园艺 | 782篇 |
植物保护 | 3860篇 |
出版年
2018年 | 731篇 |
2017年 | 775篇 |
2016年 | 749篇 |
2015年 | 707篇 |
2014年 | 751篇 |
2013年 | 2140篇 |
2012年 | 1513篇 |
2011年 | 1782篇 |
2010年 | 1224篇 |
2009年 | 1139篇 |
2008年 | 1732篇 |
2007年 | 1667篇 |
2006年 | 1619篇 |
2005年 | 1659篇 |
2004年 | 1489篇 |
2003年 | 1518篇 |
2002年 | 1444篇 |
2001年 | 1640篇 |
2000年 | 1643篇 |
1999年 | 1368篇 |
1998年 | 650篇 |
1995年 | 678篇 |
1994年 | 651篇 |
1992年 | 1376篇 |
1991年 | 1455篇 |
1990年 | 1511篇 |
1989年 | 1522篇 |
1988年 | 1436篇 |
1987年 | 1381篇 |
1986年 | 1419篇 |
1985年 | 1389篇 |
1984年 | 1158篇 |
1983年 | 1015篇 |
1982年 | 725篇 |
1981年 | 690篇 |
1980年 | 645篇 |
1979年 | 1133篇 |
1978年 | 920篇 |
1977年 | 819篇 |
1976年 | 769篇 |
1975年 | 860篇 |
1974年 | 1127篇 |
1973年 | 1064篇 |
1972年 | 1129篇 |
1971年 | 1083篇 |
1970年 | 1024篇 |
1969年 | 876篇 |
1968年 | 710篇 |
1967年 | 848篇 |
1966年 | 698篇 |
排序方式: 共有10000条查询结果,搜索用时 13 毫秒
991.
Characterization of putative Haemophilus somnus isolates from tonsils of American bison (Bison bison). 下载免费PDF全文
Three Haemophilus somnus isolates (2a, 3a, and 27b) and one H. somnus-like (13b) isolate from tonsils of commercially reared American bison were compared with 2 known H. somnus isolates from cattle, namely, 2336, shown to cause respiratory disease, and 129Pt, from the prepuce of an asymptomatic bull. All H. somnus isolates, but not the H. somnus-like isolate, required CO2 for growth. Biochemical utilization profiles were identical for bison and bovine H. somnus isolates with the exception of alpha-fucosidase production by isolate 3a. Isolate 27a varied from 2a, 2336 and 129Pt by hemolysis of bovine erythrocytes. Isolate 13b hemolyzed sheep but not bovine or bison erythrocytes and varied from other isolates in biochemical utilization tests. Outer membrane protein profiles of 2a, 3a and 27a were almost identical with those of bovine isolate 2336 and similar to that of 129Pt, but quite different from that of 13b. Western blots of bison isolates were similar to that of the virulent bovine 2336 isolate, including detection of high molecular mass antigens above 100 kDa and the 76 kDa antigens associated with bovine IgG2 Fc binding characteristic of virulent strains, as well as antigens of approximately 78, 60 and 40 kDa. Producers and veterinarians should be aware that H. somnus may be carried by bison and may have potential for causing diseases in bison similar to those described in cattle and sheep. 相似文献
992.
K. J. Shingfield N. W. Offer 《Journal of animal physiology and animal nutrition》1999,82(2-3):125-134
Introduction A number of systems based on metabolizable protein, such as that adopted in the UK (A gricultural and F ood R esearch C ouncil 1992) have been developed to improve the accuracy of protein rationing for ruminants. Quantification of microbial protein synthesis in the rumen is a fundamental requirement of all such systems. In the UK system, microbial protein supply is predicted from an estimate of fermentable metabolizable energy intake, using a correction for the effects of level of feeding on the energetic efficiency of microbial protein synthesis. Use of such an approach is however subject to considerable error due to large variations in the energetic efficiency of microbial protein synthesis (A gricultural R esearch C ouncil 1984). Consequently there is an urgent requirement for an on-farm diagnostic marker of microbial protein supply as a basis for adjusting diets to maximize efficiency of dietary nitrogen utilization by dairy cows (D ewhurst et al. 1996). Urinary purine derivative excretion has been proposed as a noninvasive index of microbial protein supply in ruminant animals (T opps and E lliot 1965). Use of this microbial marker is based on the assumption that purines entering the duodenum are essentially microbial in origin (M c A llan 1982), and that following metabolism, their derivatives are quantitatively recovered in the urine (C hen et al. 1990; V erbic et al. 1990). Purine metabolites excreted in ruminant urine are primarily derived from the metabolism of absorbed purines, but as a consequence of tissue adenosine triphosphate and nucleic acid turnover, a proportion of purine bases are not salvaged and re-utilized, but enter catabolic pathways, constituting an endogenous loss. 相似文献
993.
994.
995.
为掌握广东惠州地区供港活猪主要疫病的免疫状况,我们对供港活猪主要疫病抗体水平作了一次跟踪监测,并对免疫效果进行了分析.2012-2014年,分5次共采取了900头供港猪血清,采用ELISA方法对猪瘟、猪繁殖与呼吸障碍综合征、伪狂犬病、0型口蹄疫的抗体水平进行检测.结果显示,猪瘟抗体免疫合格率在68.9% ~78.3%之间,口蹄疫在67.2%~82.8%之间,免疫效果不理想;猪繁殖与呼吸障碍综合征抗体免疫合格率在73.9%~ 92.8%之间,伪狂犬病在86.7% ~ 93.9%之间,免疫效果较理想. 相似文献
996.
The commercial housing of African Ostriches in Germany for the breed and meat production still represents a disputed topic under the criterion of the animal's welfare. Above all critics state that the frequently wet-cold weather in Germany impairs the well-being and health of the animals. So far however there are just a few scientifically documented data about requirements for housing conditions of ostriches in Central Europe and thus hardly answers whether housing in Germany is possible under the criteria of the animal's welfare. This study tried to evaluate ostrich housing under South German climatic conditions (Rhine level), on the basis of behavioral observations of breeding ostriches. The use of the stable and the influence of different climatic parameters on the behavior were considered. In addition the behavior of 18 adult animals in 5 breeding groups from January to December 2002 was observed. Parallel various climatic data were raised. The housing of the animals took place in open stables with unrestricted pasture possibility. The ostriches reacted in their behavior to different climatic conditions. Particularly at cold weather and adverse soil conditions they used the open stable increasingly as weather protection. In addition, with increased wind velocities the animals spent more time in the stables. The daily amount of precipitation showed no influence on the frequency or duration of the stable use. Rainfall did not animate the animals to look for protection within the stable, but more to set itself on the ground in the external enclosure. The locomotion activity of the animals was strongly in dependence to the reproduction time and the territorial behavior and therefore highest in spring. On cold days the animals performed their reproduction behavior mainly in the stable. For the comfort behaviour distinct weather dependence was seen particularly for sand bathing. Warm temperatures and dry sand were the preconditions for it. Regarding the results it seems, that with the conditions existing on the examined farm, housing of ostriches under respect of animal welfare in Germany is possible. New regulations are to be demanded, adjusted to the newest level of knowledge about ostrich husbandry, with requirements for care, support, accommodation and nutrition of the animals as well as about the qualification of the owners. An occasional hobby animal husbandry limited to few single ostriches is to be rejected. Further scientific investigations at other farms, possibly also under variable climatic conditions are however necessary. 相似文献
997.
Spontaneous resolution of iatrogenic chylothorax in a cat 总被引:1,自引:0,他引:1
Greenberg MJ Weisse CW 《Journal of the American Veterinary Medical Association》2005,226(10):1667-70, 1659
Chylothorax is an uncommon condition of dogs and cats defined by the accumulation of chylous effusion within the pleural space. Chylothorax has been experimentally created in dogs and cats by ligation of the cranial vena cava and has been reported to occur spontaneously in dogs with naturally occurring obstruction of the cranial vena cava. In the cat of this report, iatrogenic chylothorax was caused by surgical ligation and transection of the left brachiocephalic vein during a tracheal resection and anastomosis procedure. The chylous effusion resolved with medical management 9 weeks after surgery. 相似文献
998.
999.
Matthew A.O. Atilola DVM PhD Joanne R. Cockshutt DVM MS Ron Mclaughlin DVM DVSc Susan M. Cochrane DVM DVSc Paul W. Pennock DVM MS 《Veterinary radiology & ultrasound》1993,34(5):321-324
Five clinically normal five year old dogs were used in this study. From a randomised table inter ver tebral discs were each injected with either collagenase or calcium chloride diluent. The surgically exposed cervical discs were injected with 50 units whereas thoracic and lumbar discs were injected under fluoroscopic guidance with 100 units of the enzyme. Postinjection radiographs revealed significant (p ≤ .05) disc space narrowing in enzyme injected discs. The cervical discs had the highest frequency of radiographic narrowing (87%) followed by the thoracic (70%) and lumbar (53%) discs. Spondylosis deformans developed at the sites of cervical enzyme injections. None of the dogs had neurologic abnormalities one year postinjection. 相似文献
1000.
van Klaveren NJ Suwankong N De Boer S van den Brom WE Voorhout G Hazewinkel HA Meij BP 《Veterinary surgery : VS》2005,34(5):450-456
OBJECTIVE: Using force plate analysis (FPA), determine ground reaction forces in dogs with degenerative lumbosacral stenosis (DLS) and evaluate the effects of lumbosacral decompressive surgery. STUDY DESIGN: Prospective clinical study. ANIMALS: Twelve dogs with DLS. METHODS: DLS was diagnosed by clinical signs, radiography, computed tomography, and/or magnetic resonance imaging. FPA was performed before surgery, and 3 days, 6 weeks, and 6 months after surgery. The mean peak braking (Fy+), peak propulsive (Fy-), and peak vertical (Fz+) forces of 8 consecutive strides were determined. The ratio between the total Fy- of the pelvic limbs and the total Fy- of the thoracic limbs (P/TFy-), reflecting the distribution of Fy-, was analyzed to evaluate any changes in locomotion pattern postoperatively. Ground reaction force data for DLS dogs were compared with data derived from 24 healthy dogs (control). RESULTS: In dogs with DLS, the propulsive forces (Fy-) of the pelvic limbs were significantly smaller than those of controls. P/TFy- was significantly smaller in dogs with DLS than in control dogs, and increased during the follow-up period, reaching normal values 6 months after surgery. CONCLUSIONS: Cauda equina compression in dogs with DLS decreases the propulsive force of the pelvic limbs and surgical treatment restores the propulsive force of the pelvic limbs in a 6-month period. CLINICAL RELEVANCE: In dogs with DLS, FPA is an effective method in evaluating the response to surgical treatment. Normal propulsive force in the pelvic limbs was restored during 6 months after decompressive surgery. 相似文献