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   1483篇
  免费   90篇
  国内免费   15篇
林业   106篇
农学   40篇
基础科学   7篇
  218篇
综合类   281篇
农作物   60篇
水产渔业   85篇
畜牧兽医   665篇
园艺   49篇
植物保护   77篇
  2022年   12篇
  2021年   21篇
  2020年   12篇
  2019年   27篇
  2018年   24篇
  2017年   33篇
  2016年   39篇
  2015年   19篇
  2014年   43篇
  2013年   70篇
  2012年   70篇
  2011年   88篇
  2010年   55篇
  2009年   64篇
  2008年   69篇
  2007年   62篇
  2006年   60篇
  2005年   71篇
  2004年   55篇
  2003年   55篇
  2002年   54篇
  2001年   23篇
  2000年   18篇
  1999年   16篇
  1998年   13篇
  1997年   14篇
  1995年   13篇
  1994年   13篇
  1993年   14篇
  1992年   17篇
  1991年   13篇
  1990年   15篇
  1989年   12篇
  1988年   10篇
  1987年   10篇
  1985年   16篇
  1983年   12篇
  1979年   26篇
  1978年   25篇
  1977年   15篇
  1976年   14篇
  1975年   13篇
  1974年   10篇
  1973年   12篇
  1972年   17篇
  1971年   14篇
  1970年   12篇
  1968年   13篇
  1967年   9篇
  1966年   10篇
排序方式: 共有1588条查询结果,搜索用时 0 毫秒
191.
The new growth retardants piproctanyl bromide (Alden or Stemtrol), dikegulac-sodium (Atrinal), PP 528 (a phenyl tetrazole compound) and 2,3-dihydro-5,6-diphenyl-1,4-oxathiin (coded UBI-P293) were compared with the established compounds chlormequat chloride (Cycocel), ancymidol (A-Rest or Reducymol) and chlorphonium chloride (Phosfon), for their ability to dwarf Mid-Century Hybrid lily cultivars ‘Enchantment’ and ‘Joan Evans’. Single compost drenches were given 2–3 weeks after transferring plants to the glasshouse.Piproctanyl bromide at high concentrations (2000 mg a.i. per plant) produced some dwarfing, as did chlorphonium chloride (at 250 mg a.i. per plant). Chlormequat chloride produced a similar response at 1250 mg a.i. per plant, but on a concentration basis ancymidol was by far the most active compound (only 0.25–0.50 mg a.i. per plant was required). Plant and flower quality was generally good with these 3 chemicals.Dikegulac-sodium reduced stem length but prevented the development of flower buds and the plants senesced. PP 528 also restricted stem extension but plant quality was unsatisfactory; increasing concentrations led to smaller florets, weaker stems and drooping leaves. UBI-P293 produced as great a reduction in stem length as did ancymidol, and 100 mg a.i. per plant was as active as 500 mg. However, as the concentration was raised there was a decrease in floret size and number.  相似文献   
192.
193.
The effect on stomatal resistance of ethylene released from ethephon sprays has been studied in 8 species of plants. Ethephon always increased stomatal resistance, but in some species only slightly. In olive and peach, increased stomatal resistance in treated plants was associated with more abscisic acid in the leaf tissues.  相似文献   
194.
195.
196.
197.
OBJECTIVE: To determine response rates and survival times for cats with lymphoma treated with the University of Wisconsin-Madison chemotherapy protocol. DESIGN: Retrospective study. ANIMALS: 38 cats with lymphoma. PROCEDURE: Medical records were reviewed, and information on age, sex, breed, FeLV and FIV infection status, anatomic form, clinical stage, and survival time was obtained. Immunophenotyping was not performed. RESULTS: Mean +/- SD age of the cats was 10.9 +/- 4.4 years. Overall median survival time was 210 days (interquartile range, 90 to 657 days), and overall duration of first remission was 156 days (interquartile range, 87 to 316 days). Age, sex, anatomic form, and clinical stage were not significantly associated with duration of first remission or survival time. Eighteen of the 38 (47%) cats had complete remission, 14 (37%) had partial remission, and 6 (16%) had no response. Duration of first remission was significantly longer for cats with complete remission (654 days) than for cats with partial remission (114 days). Median survival time for cats with complete remission (654 days) was significantly longer than median survival time for cats with partial remission (122 days) and for cats with no response (11 days). CONCLUSIONS AND CLINICAL RELEVANCE: Results suggested that a high percentage of cats with lymphoma will respond to treatment with the University of Wisconsin-Madison chemotherapy protocol. Age, sex, anatomic form, and clinical stage were not significantly associated with duration of first response or survival time, but initial response to treatment was.  相似文献   
198.
Scrapie and bovine spongiform encephalopathy (BSE) are major global concerns and the emergence of variant Creutzfeldt-Jakob disease (vCJD) has caused turmoil for blood transfusion services and hospitals worldwide. Recent reports of iatrogenic CJD (iCJD) cases following blood transfusions from Transmissible Spongiform Encephalopathies (TSE)-infected donors have fuelled this concern. Major diagnostic tests for BSE and scrapie are conducted post-mortem from animals in late stages of the disease. Although the lymphoreticular system is involved in the earlier pathogenesis of some forms of sheep scrapie and vCJD, which presents great opportunity for diagnostic development, other TSE diseases (some strains of scrapie, sporadic CJD (sCJD) and bovine BSE) do not present such a diagnostic opportunity. Thus, there is an urgent need for pre-mortem tests that differentiate between healthy and diseased individuals at early stages of illness, in accessible samples such as blood and urine using less invasive procedures. This review reports on the current state of progress in the development and use of prion and non-prion biomarkers in the diagnosis of TSE diseases. Some of these efforts have concentrated on improving the sensitivity of PrPSc detection to allow in vivo diagnosis at low abundances of PrPSc whilst others have sought to identify non-prion protein biomarkers of TSE disease, many of which are still at early stages of development. In this review we comment upon the limitations of prion based tests and review current research on the development of tests for TSE that rely on non-prion disease markers in body fluids that may allow preclinical disease diagnosis.  相似文献   
199.
OBJECTIVE: To determine the pharmacokinetics of carvedilol administered IV and orally and determine the dose of carvedilol required to maintain plasma concentrations associated with anticipated therapeutic efficacy when administered orally to dogs. ANIMALS: 8 healthy dogs. PROCEDURES: Blood samples were collected for 24 hours after single doses of carvedilol were administered IV (175 microg/kg) or PO (1.5 mg/kg) by use of a crossover nonrandomized design. Carvedilol concentrations were detected in plasma by use of high-performance liquid chromatography. Plasma drug concentration versus time curves were subjected to noncompartmental pharmacokinetic analysis. RESULTS: The median peak concentration (extrapolated) of carvedilol after IV administration was 476 ng/mL (range, 203 to 1,920 ng/mL), elimination half-life (t(1/2)) was 282 minutes (range, 19 to 1,021 minutes), and mean residence time (MRT) was 360 minutes (range, 19 to 819 minutes). Volume of distribution at steady state was 2.0 L/kg (range, 0.7 to 4.3 L/kg). After oral administration of carvedilol, the median peak concentration was 24 microg/mL (range, 9 to 173 microg/mL), time to maximum concentration was 90 minutes (range, 60 to 180 minutes), t(1/2) was 82 minutes (range, 64 to 138 minutes), and MRT was 182 minutes (range, 112 to 254 minutes). Median bioavailability after oral administration of carvedilol was 2.1% (range, 0.4% to 54%). CONCLUSIONS AND CLINICAL RELEVANCE: Although results suggested a 3-hour dosing interval on the basis of MRT, pharmacodynamic studies investigating the duration of beta-adrenoreceptor blockade provide a more accurate basis for determining the dosing interval of carvedilol.  相似文献   
200.
OBJECTIVE: To determine the outcome and effect of surgical technique on limb function after surgery for rupture of the cranial cruciate ligament (RCCL) and injury to the medial meniscus in Labrador Retrievers. STUDY DESIGN: Prospective clinical study. ANIMALS: 131 Labrador Retrievers with unilateral RCCL and injury to the medial meniscus and 17 clinically normal Labrador Retrievers. PROCEDURE: Affected dogs had partial or complete medial meniscectomy and lateral suture stabilization (LSS), intracapsular stabilization (ICS), or tibial plateau leveling osteotomy (TPLO). Limb function was measured before surgery and 2 and 6 months after surgery. Treated dogs were evaluated to determine the probability that they could be differentiated from clinically normal dogs and tested to determine the likelihood that they achieved improvement. RESULTS: No difference was found between LSS or TPLO groups, but dogs treated with ICS had significantly lower ground reaction forces at 2 and 6 months. Compared with clinically normal dogs only, 14.9% of LSS-, 15% of ICS-, and 10.9% of TPLO-treated dogs had normal limb function. Improvement was seen in only 15% of dogs treated via ICS, 34% treated via TPLO, and 40% treated via LSS. CONCLUSIONS AND CLINICAL RELEVANCE: Surgical technique can influence limb function after surgery. Labrador Retrievers treated via LSS, ICS, or TPLO for repair for of RCCL and medial meniscal injury managed with partial or complete meniscectomy infrequently achieve normal function. Results of LSS and TPLO are similar and superior to ICS.  相似文献   
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