全文获取类型
收费全文 | 51586篇 |
免费 | 692篇 |
国内免费 | 1229篇 |
专业分类
林业 | 3208篇 |
农学 | 1831篇 |
基础科学 | 834篇 |
5365篇 | |
综合类 | 13024篇 |
农作物 | 2953篇 |
水产渔业 | 647篇 |
畜牧兽医 | 22477篇 |
园艺 | 1254篇 |
植物保护 | 1914篇 |
出版年
2023年 | 449篇 |
2022年 | 361篇 |
2021年 | 346篇 |
2020年 | 384篇 |
2019年 | 488篇 |
2018年 | 635篇 |
2017年 | 227篇 |
2016年 | 503篇 |
2015年 | 537篇 |
2014年 | 960篇 |
2013年 | 790篇 |
2012年 | 3003篇 |
2011年 | 3374篇 |
2010年 | 1294篇 |
2009年 | 913篇 |
2008年 | 2740篇 |
2007年 | 2872篇 |
2006年 | 3052篇 |
2005年 | 2406篇 |
2004年 | 2346篇 |
2003年 | 2436篇 |
2002年 | 2402篇 |
2001年 | 1667篇 |
2000年 | 1804篇 |
1999年 | 895篇 |
1998年 | 216篇 |
1997年 | 190篇 |
1996年 | 210篇 |
1995年 | 284篇 |
1994年 | 392篇 |
1993年 | 561篇 |
1992年 | 700篇 |
1991年 | 814篇 |
1990年 | 860篇 |
1989年 | 613篇 |
1988年 | 1198篇 |
1987年 | 1260篇 |
1986年 | 946篇 |
1985年 | 1095篇 |
1984年 | 1182篇 |
1983年 | 855篇 |
1982年 | 861篇 |
1981年 | 638篇 |
1980年 | 419篇 |
1979年 | 286篇 |
1978年 | 149篇 |
1960年 | 138篇 |
1959年 | 174篇 |
1958年 | 135篇 |
1957年 | 187篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
992.
Three olfactometric methods (frequency of detection, time--intensity method, and aroma extract dilution analysis) were used to evaluate the main odorants of three musts obtained from French--Romanian hybrids (Valerien, Admira, and Brumariu). The three methods allow detection of the same odor-active compounds. The results obtained from these methods were closely related. Nineteen odor-active compounds were detected, and 13 were identified. The three methods showed the importance of an unidentified compound with a grape and grape juice aroma note in the three musts. Among the other compounds, 3-hexen-1-al, (E,Z)-2,6-nonadien-1-ol, and 1-ccten-3-one seemed to contribute actively to the odor of Valerien must. 3-(Methylthio)propanal and hexanal were contributors to the Admira and Brumariu odor. Phenylacetaldehyde was one of the main odor-active compounds in must from Admira. 相似文献
993.
994.
Long-term storage of information in DNA 总被引:1,自引:0,他引:1
995.
Koenig R 《Science (New York, N.Y.)》2001,293(5533):1251-1253
996.
Yazawa M Okuda M Setoguchi A Iwabuchi S Nishimura R Sasaki N Masuda K Ohno K Tsujimoto H 《American journal of veterinary research》2001,62(10):1539-1543
OBJECTIVE: To measure telomere length and telomerase activity in naturally occurring canine mammary gland tumors. SAMPLE POPULATION: 27 mammary gland tumor specimens obtained during resection or necropsy and 12 mammary gland tissue specimens obtained from healthy (control) dogs. PROCEDURE: Telomere length in tissue specimens was measured by use of restriction endonuclease digestion and Southern blot analysis. Telomerase activity was measured by use of a telomeric repeat amplification protocol assay. RESULTS: Telomere length in mammary gland tumors ranged from 11.0 to 21.6 kilobase pairs (kbp; mean +/- SEM, 14.5+/-0.5 kbp) but did not differ among tumor types. Telomeres in mammary gland tumors were slightly shorter than in normal tissue specimens, but telomere length could not be directly compared between groups, because mean age of dogs was significantly different between groups. Age was negatively correlated with telomere length in control dogs but was not significantly correlated with length in affected dogs. Telomerase activity was detected in 26 of 27 mammary gland tumors and in 4 of 12 normal tissue specimens. However, telomerase activity and telomere length were not correlated in tumor specimens. CONCLUSIONS AND CLINICAL RELEVANCE: Telomere length is maintained in canine mammary gland tumors regardless of the age of the affected dog. Measurement of telomere length may be a useful tool for monitoring the in vivo effects of telomerase inhibitors in dogs with tumors. 相似文献
997.
Schumann RJ Morgan MS Glass R Arlian LG 《American journal of veterinary research》2001,62(9):1344-1348
OBJECTIVE: To identify the major allergenic proteins from the 3 main species of dust mites to which dogs react (Dermatophagoides farinae, D. pteronyssinus, and Euroglyphus maynei) and evaluate the potential cross-reactivity of dust mite allergens with antigens from the ectoparasitic mite Sarcoptes scabiei var canis. SAMPLE POPULATION: Sera from 83 dogs with atopic dermatitis. PROCEDURE: Sodium dodecylsulfate-polyacrylamide gel electrophoresis and immunoblotting using serum from atopic dogs was used to identify IgE-binding proteins in extracts of the 4 mite species. RESULTS: Sera of atopic dogs contained IgE against 23, 17, 25, and 17 allergens from D. farinae, D. pteronyssinus, E. maynei, and S. scabiei, respectively. Unlike the situation for humans, the major allergens for dogs are mostly proteins that are larger than 90 kd molecular weight. Dermatophagoides farinae and E. maynei appear to be more allergenic for dogs than is D. pteronyssinus. Some dogs with serum IgE against dust mites also had IgE against antigens of S. scabiei var canis. CONCLUSIONS AND CLINICAL RELEVANCE: Multiple dust mite allergens induce an IgE response in dogs. These allergens are mostly greater than 90 kd molecular weight. 相似文献
998.
Lunn DP Hussey S Sebing R Rushlow KE Radecki SV Whitaker-Dowling P Youngner JS Chambers TM Holland RE Horohov DW 《Journal of the American Veterinary Medical Association》2001,218(6):900-906
OBJECTIVE: To determine safety, efficacy, and immunogenicity of an intranasal cold-adapted modified-live equine influenza virus vaccine administered to ponies following induction of exercise-induced immunosuppression. DESIGN: Prospective study. ANIMALS: Fifteen 9- to 15-month old ponies that had not had influenza. PROCEDURE: Five ponies were vaccinated after 5 days of strenuous exercise on a high-speed treadmill, 5 were vaccinated without undergoing exercise, and 5 were not vaccinated or exercised and served as controls. Three months later, all ponies were challenged by nebulization of homologous equine influenza virus. Clinical and hematologic responses and viral shedding were monitored, and serum and nasal secretions were collected for determination of influenza-virus-specific antibody isotype responses. RESULTS: Exercise caused immunosuppression, as indicated by depression of lymphocyte proliferation in response to pokeweed mitogen. Vaccination did not result in adverse clinical effects, and none of the vaccinated ponies developed clinical signs of infection following challenge exposure. In contrast, challenge exposure caused marked clinical signs of respiratory tract disease in 4 control ponies. Vaccinated and control ponies shed virus after challenge exposure. Antibody responses to vaccination were restricted to serum IgGa and IgGb responses in both vaccination groups. After challenge exposure, ponies in all groups generated serum IgGa and IgGb and nasal IgA responses. Patterns of serum hemagglutination inhibition titers were similar to patterns of IgGa and IgGb responses. CONCLUSIONS AND CLINICAL RELEVANCE: Results suggested that administration of this MLV vaccine to ponies with exercise-induced immunosuppression was safe and that administration of a single dose to ponies provided clinical protection 3 months later. 相似文献
999.
Takahashi T Hiraga A Ohmura H Kai M Jones JH 《Journal of the American Veterinary Medical Association》2001,218(9):1462-1464
OBJECTIVE: To determine the frequency of epistaxis during or after racing among racehorses and identify factors associated with development of epistaxis. DESIGN: Retrospective study. SAMPLE POPULATION: 247,564 Thoroughbred and 4,045 Anglo-Arab race starts. PROCEDURE: Race start information (breed, age, sex, racing distance, and race type) was obtained for Thoroughbred and Anglo-Arab horses racing in Japan Racing Association-sanctioned races between 1992 and 1997. All horses that raced were examined by a veterinarian within 30 minutes of the conclusion of the race; any horse that had blood at the nostrils was examined with an endoscope. If blood was observed in the trachea, epistaxis related to exercise-induced pulmonary hemorrhage (EIPH) was diagnosed. RESULTS: Epistaxis related to EIPH was identified following 369 race starts (0.15%). Frequency of EIPH-related epistaxis was significantly associated with race type, age, distance, and sex. Epistaxis was more common following steeplechase races than following flat races, in older horses than in horses that were 2 years old, following races < or =1,600 m long than following races between 1,601 and 2,000 m long, and in females than in sexually intact males. For horses that had an episode of epistaxis, the recurrence rate was 4.64%. CONCLUSIONS AND CLINICAL RELEVANCE: Results suggested that frequency of EIPH-related epistaxis in racehorses is associated with the horse's age and sex, the type of race, and the distance raced. The higher frequency in shorter races suggests that higher intensity exercise of shorter duration may increase the probability of EIPH. 相似文献
1000.