全文获取类型
收费全文 | 153561篇 |
免费 | 9120篇 |
国内免费 | 812篇 |
专业分类
林业 | 6379篇 |
农学 | 5407篇 |
基础科学 | 1204篇 |
19024篇 | |
综合类 | 27303篇 |
农作物 | 5750篇 |
水产渔业 | 7743篇 |
畜牧兽医 | 79121篇 |
园艺 | 2128篇 |
植物保护 | 9434篇 |
出版年
2020年 | 1379篇 |
2019年 | 1728篇 |
2018年 | 2526篇 |
2017年 | 2908篇 |
2016年 | 2629篇 |
2015年 | 2375篇 |
2014年 | 2777篇 |
2013年 | 5958篇 |
2012年 | 5036篇 |
2011年 | 6159篇 |
2010年 | 4132篇 |
2009年 | 3981篇 |
2008年 | 5724篇 |
2007年 | 5405篇 |
2006年 | 5115篇 |
2005年 | 4609篇 |
2004年 | 4264篇 |
2003年 | 4359篇 |
2002年 | 4019篇 |
2001年 | 5076篇 |
2000年 | 4980篇 |
1999年 | 3885篇 |
1998年 | 1585篇 |
1997年 | 1584篇 |
1996年 | 1378篇 |
1995年 | 1573篇 |
1994年 | 1430篇 |
1993年 | 1411篇 |
1992年 | 2986篇 |
1991年 | 3249篇 |
1990年 | 3080篇 |
1989年 | 3065篇 |
1988年 | 2739篇 |
1987年 | 2794篇 |
1986年 | 2837篇 |
1985年 | 2605篇 |
1984年 | 2205篇 |
1983年 | 1873篇 |
1982年 | 1292篇 |
1979年 | 1923篇 |
1978年 | 1533篇 |
1976年 | 1296篇 |
1975年 | 1474篇 |
1974年 | 1770篇 |
1973年 | 1719篇 |
1972年 | 1626篇 |
1971年 | 1555篇 |
1970年 | 1543篇 |
1969年 | 1478篇 |
1967年 | 1330篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
A porcine in vitro fertilization (IVF) system and seminal quality parameters of frozen–thawed boar semen were used to assess the effectiveness of two different thawing rates of frozen boar semen, and to address the question of whether differences between fertility of ejaculates could be predicted in a limited field trial. In the first experiment, two thawing procedures were analysed (37°C, 30 s; 50°C, 12 s) and no differences in sperm quality were found. However, when the procedure was 50°C, 12 s the IVF results showed a higher number of sperm per penetrated oocyte and a near 10 points higher rate of pronuclear formation. In the second experiment, the fertility results obtained in the limited field trial show to be efficient enough for application in a commercial use, especially for three of the employed boars (fertility ≥80%). In this limited study, the conventional seminal parameters are not accurate enough to discriminate good and bad boars in relation to fertility. On the contrary, parameters of in vitro penetrability are more precise to predict subsequent fertilities. As conclusion, the IVF fertilization system seems to be a good tool to evaluate the quality of frozen–thawed boar semen previous to its commercial way, to verify the bank semen storage quality and a good way to assay new sperm freezing procedures, as it is the more precise evaluating method in estimating the potential fertilizing ability. 相似文献
102.
Jennifer L Davis 《Veterinary Clinics of North America: Equine Practice》2003,19(3):765-778
In summary, peritonitis in the horse is a potentially life-threatening disease that must be treated promptly and aggressively. Therapy should be aimed at reducing systemic shock and hypovolemia, correction of the primary cause, antibiotic and anti-inflammatory therapy, and abdominal drainage and lavage. The prognosis depends on the ability to diagnose and treat the underlying cause and prevent the development of complications. Mortality rates can be as high as 59.7%, with horses developing postoperative peritonitis having a 56% mortality rate. Long-term complications like adhesion formation or internal abscesses may further reduce the survival rate. The prognosis is best determined by an early and quick response to aggressive treatment. 相似文献
103.
W Petchpoo P Tan-ariya V Boonsaeng C R Brockelman P Wilairat S Panyim 《Veterinary parasitology》1992,42(3-4):189-198
A genomic library of Babesia bovis DNA from the Mexican strain M was constructed in plasmid pUN121 and cloned in Escherichia coli. Several recombinants which hybridized strongly to radioactively labeled B. bovis genomic DNA in an in situ screening were selected and further analyzed for those which specifically hybridized to B. bovis DNA. It was found that pMU-B1 had the highest sensitivity, detecting 25 pg of purified B. bovis DNA, and 300 parasites in 10 microliters of whole infected blood, or 0.00025% parasitemia. pMU-B1 contained a 6.0 kb B. bovis DNA insert which did not cross-hybridize to Babesia bigemina, Trypanosoma evansi, Plasmodium falciparum, Anaplasma marginale, Boophilus microplus and cow DNA. In the Southern blot analysis of genomic DNA, pMU-B1 could differentiate between two B. bovis geographic isolates, Mexican strain M and Thai isolate TS4. Thus, the pMU-B1 probe will be useful in the diagnosis of Babesia infection in cattle and ticks, and in the differentiation of B. bovis strains. 相似文献
104.
Use of Echinococcus granulosus worm antigens for immunodiagnosis of E. granulosus infection in dogs.
Echinococcus granulosus worm excretory/secretory antigens (WES) were used in ELISA for diagnosis of E. granulosus infection in dogs and compared with protoscolex somatic antigens (PSM). Sera from 224 dogs were tested. There was no correlation between ELISA absorbance values and E. granulosus worm burdens using either antigen. There was a significant linear relationship between absorbance values of sera tested in the ELISA using WES (W-ELISA) and the ELISA using PSM (P-ELISA). However, there was a small but significant difference between the absorbance values of the sera tested against the two antigens. Western blot analysis of WES using sera from E. granulosus-infected and uninfected dogs revealed antigenic components of relative molecular mass (Mr) larger than 94,000, Mr 94,000-68,000 and Mr 43,000-39,000 in worms, and these were specific for E. granulosus and not identified in PSM; these antigenic differences may be responsible for differences in reactivity in ELISA. The sensitivities of W-ELISA and P-ELISA were 80.8% and 75.6%, respectively. The specificities of W-ELISA and P-ELISA were 93.7% and 97.9%, respectively. The reduced specificity in W-ELISA was mainly attributable to increased background reactivity of sera from Taenia hydatigena-infected dogs. Despite the reduction in specificity, both ELISAs are valuable epidemiological tools to determine the prevalence of antibody to E. granulosus in dog populations and to monitor the success of hydatid control campaigns. 相似文献
105.
M Washizu K Kobayashi K Misaka T Hayashi G Kinoshita M Kondo S Aoki H Orima T Washizu 《The Journal of veterinary medical science / the Japanese Society of Veterinary Science》1992,54(5):1051-1053
A 2-year-old female Japanese domestic cat weighing 3.6 kg was presented due to marked abdominal distention and was diagnosed as hepatic cyst. The bile acid concentration of the hepatic cyst was as low as the serum bile acid concentration. The membrane of the cysts was excised from the edge of the compressed hepatic tissue and no other surgical manipulation was performed. This surgical procedure is simple and quick compared to hepatic lobectomy, however, it is necessary to evaluate the fluid of the cyst before performing this procedure. 相似文献
106.
J. Gonzalez-Soriano E. Rodriguez-Veiga P. Martinez-Sainz S. Mayayo-Vicente P. Marin-Garcia 《Anatomia, histologia, embryologia》1995,24(1):61-65
As in the number of mammals, the most prominent feature of the ganglion-cell layer in the retina of the German shepherd dog is the sharp increase in the density of ganglion cells in the central area. There is an area of maximum density and also a ‘cat-like’ visual streak, located dorsal to the optic disc. The isodensity lines of ganglion-cell distribution is roughly concentric. Their values vary from 5300-13 000 cells/mm2 in the central area, with the cells densely packed, to 1000 cells/mm2 or less in the periphery, where the cells are sparsely distributed. There were some individual differences amongst the animals studied, although all of them were pure-bred dogs. This suggests that the configuration of the retina in the canine species is not only dependent on the breed itself but also on some other parameters such as phylogenetic heritage, environment, aptitude, lifestyle, or even training. 相似文献
107.
L. Pülschen 《Journal of Agronomy and Crop Science》1992,168(4):249-254
Mixed cropping of leguminous underseed species and cereal crops may increase productivity and serve some additional purposes. Two leguminous weed species which are widely distributed in annual crops of the Ethiopian highlands have been studied with varying coverage in greenhouse trials in Ethiopia with regard to their suitability as underseeds and with wheat ( Triticum turgidum [L.] Thell. var. durum [Desf.] MacKey) as a main crop. The competitive effects of Scorpiurus muricatus L. on the grain yield of wheat were smaller than those of Medicago polymorpha L. (-14.1 % and -23.6 % respectively, compared with the underseed free control) which is mainly ascribed to differences in their speed of development and shoot height. The residual effects of the underseed's root masses on the grain yield of the successive teff crop (Eragrostis tef [Zucc] Trotter) were significantly higher with Scorpiurus muricatus (+99.3 %) than with Medicago polymorpha (+63.6 %). The results are discussed with regard to the specific site conditions in the cereal-dominated cropping systems of the Ethiopian highlands. 相似文献
108.
L G Rickard G L Zimmerman E P Hoberg P W Lockwood D W Weber R Miller 《Veterinary parasitology》1989,33(2):125-133
The effectiveness of the morantel sustained release trilaminate (MSRT) in controlling gastrointestinal nematodes through a grazing season was evaluated using 60 yearling beef stocker calves randomly divided into 2 groups of 30 animals each. In April 1985, the calves comprising the treatment group each received an MSRT designed to release morantel tartrate continuously for 90 days while those of the control group remained unmedicated. All animals were weighed and samples of rectal feces were taken at 14-day intervals, beginning on Day 0, until trial termination (Day 168). At trial termination, 10 control and 10 treated calves were necropsied for recovery of gastrointestinal nematodes. Three sets of parasite-na?ve tracer calves were utilized to evaluate the initial, interim and final levels of pasture contamination by nematode larvae. Overall, the use of the MSRT resulted in a 75.5% reduction (P less than 0.001) in output of nematode eggs from the principals, an 81.8% reduction (P less than 0.001) in numbers of gastrointestinal nematodes in principals (at trial termination), and a 96.9% reduction (P less than 0.05) of pasture larval nematode contamination (as indirectly indicated by parasite burdens in tracer calves). The mean weight advantage of treated calves was 16.6 kg per head (P less than 0.001). 相似文献
109.
Holly L. Jordan DVM Carol B. Grindem DVM PhD Edward B. Breitschwerdt DVM 《Journal of veterinary internal medicine / American College of Veterinary Internal Medicine》1993,7(5):261-265
The prevalence of feline thrombocytopenia (<200,000 platelets/L) at North Carolina State University, College of Veterinary Medicine Teaching Hospital, from January 1985 to March 1990, was 1.2% (41/3300). Cats were divided into six categories based on clinical diagnoses: 29% (12/41) had infectious disease, 20% (8/41) had neoplasia, 7% (3/41) had cardiac disease, 2% (1/41) had primary immune-mediated disease, 22% (9/41) had multiple diseases, and 20% (8/41) had disorders of unknown etiology. The mean platelet count for all thrombocytopenic cats was 52,000/μL ± 46,000/μL (1 SD) with a range of 1000–190,000/μL. No significant differences were found between groups with respect to platelet count, packed cell volume, or white blood cell count, though anemia and leukopenia were common among the cats as a whole. Bleeding disorders (hemorrhage or thrombosis) were observed in 29% (12/41) of thrombocytopenic cats and were more likely to be associated with neoplasia, cardiac disease, and platelet counts less than or equal to 30,000/μL. Disseminated intravascular coagulopathy was diagnosed in 12% (5/41) of the cats. Infections and/or neoplasia affecting the bone marrow were the most common diseases associated with thrombocytopenia. Feline leukemia virus and myeloproliferative neoplasia accounted for approximately 44% (18/41) of the specific diagnoses in thrombocytopenic cats. (Journal of Veterinary Internal Medicine 1993; 7:261–265. Copyright © 1993 by the American College of Veterinary Internal Medicine.) 相似文献
110.
Daniel J. Burba DVM Michael A. Collier DVM Lawrence E. Default PhD Olivia Hanson-Painton PhD Harold C. Thompson Jr. Claude L. Holder 《Journal of Equine Veterinary Science》1993,13(12):696-703
The uptake and distribution of intramuscularly (IM) administered tritium-labeled polysulfated glycosaminoglycan (3H-PSGAG) in serum, synovial fluid, and articular cartilage of eight horses was quantitated, and hyaluronic acid (HA) concentration of the middle carpal joint was evaluated in a pharmacokinetic study. A full-thickness articular cartilage defect, created on the distal articular surface of the left radial carpal bone of each horse served as an osteochondral defect model. 3H-PSGAG (500 mg) was injected IM, between 14 and 35 days after creation of the defects. Scintillation analysis of serum and synovial fluid, collected from both middle carpal joints at specific predetermined times up to 96 hours post-injection, revealed mean 3H-PSGAG concentrations peaked at 2 hours post-injection. 3H-PSGAG was detected in cartilage and subchondral bone 96 hours post-injection in samples from all eight horses. There were no statistically significant differences in 3H-PSGAG concentration of synovial fluid or cartilage between cartilage defect and control (right middle carpal) joints.
HA assay of synovial fluid revealed concentrations significantly increased at 24, 48, and 96 hours post-injection in both joints. The concentration nearly doubled 48 hours post-injection. However, no statistically significant differences were found between synovial concentrations of HA in cartilage defect and control joints.
3H-PSGAG administered IM to horses, was distributed in the blood, synovial fluid, and articular cartilage. HA concentrations in synovial fluid increased after IM administration of polysulfated glycosaminoglycan. 相似文献