首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   196532篇
  免费   10781篇
  国内免费   132篇
林业   7367篇
农学   5819篇
基础科学   1349篇
  22844篇
综合类   35615篇
农作物   7250篇
水产渔业   9528篇
畜牧兽医   101948篇
园艺   2371篇
植物保护   13354篇
  2018年   2426篇
  2017年   2622篇
  2016年   2523篇
  2015年   2195篇
  2014年   2677篇
  2013年   7310篇
  2012年   5021篇
  2011年   6287篇
  2010年   3977篇
  2009年   4072篇
  2008年   6170篇
  2007年   5815篇
  2006年   5695篇
  2005年   5274篇
  2004年   5111篇
  2003年   5152篇
  2002年   4943篇
  2001年   6134篇
  2000年   5967篇
  1999年   4779篇
  1998年   1928篇
  1997年   2008篇
  1996年   1886篇
  1995年   2307篇
  1994年   2117篇
  1993年   2014篇
  1992年   4235篇
  1991年   4442篇
  1990年   4397篇
  1989年   4399篇
  1988年   4089篇
  1987年   4212篇
  1986年   4342篇
  1985年   4189篇
  1984年   3450篇
  1983年   3053篇
  1982年   2147篇
  1981年   1955篇
  1979年   3169篇
  1978年   2646篇
  1977年   2266篇
  1976年   2092篇
  1975年   2206篇
  1974年   2905篇
  1973年   2930篇
  1972年   2854篇
  1971年   2569篇
  1970年   2433篇
  1969年   2252篇
  1967年   1945篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
This retrospective study evaluated the incidence of meniscal injury in cats with cranial cruciate ligament (CCL) ruptures. Medical records for cats diagnosed with CCL ruptures treated by a lateral fabellotibial suture (LFS) were reviewed for signalment, history, physical examination and surgical findings. Ninety-five cats (98 stifles) met the inclusion criteria. The incidence of meniscal injuries in feline CCL deficient stifles was 67%. Isolated medial meniscal injuries were found in 55 stifles (56%), isolated lateral meniscal injuries were found in 5 stifles (5%), and lateral and medial meniscal injuries were found in 6 stifles (6%). There was no correlation between the presence of a meniscal injury and age, breed, sex, weight, duration of lameness, presence of concurrent medial patellar luxation, degree of degenerative joint disease, or presenting side of lameness. Given the high rate of meniscal pathology in cats with CCL ruptures, exploratory surgery for meniscal assessment and concurrent stifle stabilization should be considered in feline patients.  相似文献   
992.
Passive immunization studies were conducted to determine the role of specific antibodies in immunity to Streptococcus ictaluri. Adult channel catfish (Ictalurus punctatus) were injected i.p. with tryptic soy broth as control or with 1.5 × 10(7)colony-forming units (cfu) S. ictaluri/fish at 0, 30, and 60 d, and serum was collected 90 d after the original challenge. Fish were passively immunized by i.p. injection with serum from the tryptic soy broth (TSB) control group, anti-S. ictaluri serum from fish immunized three times and sampled at 90 d (SSI), or heat-inactivated anti-S. ictaluri serum from fish immunized three times and sampled at 90 d (HISSI). These passively immunized fish were then challenged 72 h later with 1.5 × 10(8)cfu S. ictaluri/fish. Over 21 d, the mean cumulative percent survival was 43.3 (TSB), 63.3 (SSI), and 50.0 (HISSI). A significant difference in cumulative percent survival was noted between the TSB and the HISSI groups, and significant differences were noted between these groups and the SSI group. Serum obtained from immunized fish 72 h after passive immunization exhibited increased anti-S. ictaluri antibody levels. Twenty-one days after the challenge, the HISSI and SSI group antibody levels significantly increased above their corresponding pre-challenge levels. No significant (r(2)=0.0806; P<0.5985) correlation between increased pre-challenge specific serum antibody levels and survival after challenge was demonstrated when analyzing the control and passive immunization groups. The results indicate that both specific anti-S. ictaluri antibodies and non-specific immune responses are important for protection against S. ictaluri.  相似文献   
993.
994.
This study describes the results of ultrasonographic examination of the rumen in 30 healthy Saanen goats. A linear or convex transducer with a variable frequency of 5 to 13 MHz was used to scan standing, non-sedated goats. The location and size of the rumen, the distance between the wall of the rumen and abdominal wall and the appearance and size of the gas, fibre mat and fluid layers of the ruminal contents were assessed. The rumen was seen as a large organ medial to the left abdominal wall. The wall of the rumen appeared as a thick echogenic line. The longitudinal groove was seen as an echogenic notch, which divided the rumen into the dorsal and ventral sacs. The rumen could be visualized from the 9th to 12th intercostal space (ICS) and flank on the left side in all the goats. The rumen was largest in the 12th ICS at 41.6 ± 5.13 cm and smallest in the 8th ICS at 11.3 ± 4.29 cm. The dorsal sac of the rumen was largest in the left cranial flank (17.4 ± 4.43 cm) and the ventral sac was largest in the 12th ICS on the left (29.1 ± 6.03 cm). In the cranial left flank, the rumen was situated immediately adjacent to the abdominal wall in all the goats. The spleen was located between the rumen and abdominal wall in the 8th to 12 th ICS in many of the goats. The gas, fibre mat and fluid layers of the ruminal contents could be visualized in all the goats. The gas layer was 9.9 ± 3.05 cm, the fibre mat layer 16.0 ± 4.55 cm and the fluid layer 12.2 ± 5.57 cm.  相似文献   
995.
Understanding the inherent radiosensitivity and repair capacity of canine transitional cell carcinoma (TCC) can aid in optimizing radiation protocols to treat this disease. The objective of this study was to evaluate the parameters surviving fraction at 2 Gy (SF(2) ), α/β ratio and capacity for sublethal damage repair (SLDR) in response to radiation. Dose-response and split-dose studies were performed using the clonogenic assay. The mean SF(2) for three established TCC cell lines was high at 0.61. All the three cell lines exhibited a low to moderate α/β ratio, with the mean being 3.27. Two cell lines exhibited statistically increased survival at 4 and 24 h in the dose-response assay. Overall, our results indicate that the cell lines are moderately radioresistant, have a high repair capacity and behave similarly to a late-responding normal tissue. These findings indicate that the radiation protocols utilizing higher doses with less fractionation may be more effective for treating TCC.  相似文献   
996.
Questionnaires completed by pet owners are widely used instruments to monitor adverse gastrointestinal (GI) effects in the owners' animals undergoing chemotherapy and for reporting toxicoses in clinical trials; however, no questionnaires have been formally evaluated. This study compares two questionnaire-based evaluations of adverse GI events: a basic, open-ended questionnaire and a detailed questionnaire modelled after the grading in the Veterinary Co-operative Oncology Group-Common Terminology Criteria for Adverse Events (VCOG-CTCAE). Owners completed both questionnaires after their dog or cat received moderately emetogenic chemotherapy. Results were used to derive toxicity grades for anorexia, vomiting and diarrhoea. We evaluated 123 pairs of questionnaires. Disagreement in grade of anorexia, vomiting and diarrhoea was found in 24, 7 and 13% of paired questionnaires, respectively (κ = 0.63, 0.83 and 0.71, respectively). Although 'good' to 'very good' agreement was found, the potential for only 'fair' agreement between questionnaire methods is of concern and suggests a need to adopt a standardized form.  相似文献   
997.
Multi-agent chemotherapy successfully induces remission in most naïve, high-grade canine lymphoma patients; however, disease recurrence is common. MOPP (mechlorethamine, vincristine, procarbazine, and prednisone) is an effective rescue protocol used to re-induce remission, but is associated with gastrointestinal toxicity and can be a less desirable option for patients that previously failed vincristine-containing protocols. Therefore, alternative members of the vinca alkaloid family, such as vinblastine, could be potentially advantageous as substitutes for vincristine to reduce gastrointestinal toxicity and chemoresistance. The objective of this study was to report the clinical outcomes and toxicity of 36 dogs with relapsed or refractory multicentric lymphoma treated with a modified MOPP protocol whereby vincristine was replaced with vinblastine (MVPP). The overall response rate to MVPP was 25% with a median progression free survival of 15 days and a median overall survival of 45 days. MVPP at the prescribed doses resulted in modest and transient clinical benefit, but was well tolerated with no treatment delays or hospitalizations secondary to side effects. Given the minimal toxicity, dose intensification could be considered to improve clinical responses.  相似文献   
998.
A method is described for production of an equine anti-bovine leukocyte serum (EABLS). Leukocytes were harvested from the milk of cow's udders which had been irritated with endotoxin. The washed leukocytes as antigens were administered to 2 horses in a series of subcutaneous and intravenous injections. There was a variably progressive increase in total serum proteins and a decrease in albumin/blobulin ratios, but the most pronounced change was an increase in beta2-globulins. Accompanying these changes was an increase in the number of precipitin lines as shown by Ouchterlony analysis. Four old cows and 2 calves were intravenously given a 50- and 20-ml dose, respectively, of the EABLS. Two of the cows and 1 of the calves were given the EABLS which had been heated to 56 C for 30 minutes. Both calves and the 2 cows given heated EABLS and 1 cow given unheated EABLS developed marked neutropenia within the 1st hour. The 4th cow given unheated EABLS developed only slight neutropenia. It was concluded that there may be variation in the individual animal's susceptibility to the neutropenia-inducing activity of EABLS.  相似文献   
999.
Six epizootics of encephalomyeltis in suckling pigs in Minnesota were attributed to infection with hemagglutinating encephalomyelitis virus. The disease occurred in 74 litters of pigs and was characterized by sudden onset of tremors, inappetence, weakness, atazia, and hyperesthesia, with high morbidity and case fatality rate. Pathologic changes consisted of marked nonsuppurative, nondemyelinating encephalomyelitis characterized by perivascular mononuclear cuffing, gliosis, neuronal death, and satellitosis. Clinical disease was limited principally to suckling pigs during a single farrowing period and did not recur in the herds involved during the ensuing 18 months.  相似文献   
1000.
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号