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   73962篇
  免费   4191篇
  国内免费   35篇
林业   3197篇
农学   2415篇
基础科学   474篇
  8727篇
综合类   12152篇
农作物   2838篇
水产渔业   3573篇
畜牧兽医   38894篇
园艺   847篇
植物保护   5071篇
  2018年   973篇
  2017年   1082篇
  2016年   1011篇
  2015年   857篇
  2014年   1057篇
  2013年   2768篇
  2012年   1979篇
  2011年   2288篇
  2010年   1560篇
  2009年   1584篇
  2008年   2351篇
  2007年   2249篇
  2006年   2051篇
  2005年   1985篇
  2004年   1864篇
  2003年   2002篇
  2002年   1817篇
  2001年   2252篇
  2000年   2195篇
  1999年   1754篇
  1998年   726篇
  1997年   786篇
  1996年   702篇
  1995年   878篇
  1994年   745篇
  1993年   751篇
  1992年   1511篇
  1991年   1648篇
  1990年   1620篇
  1989年   1628篇
  1988年   1507篇
  1987年   1470篇
  1986年   1543篇
  1985年   1460篇
  1984年   1278篇
  1983年   1070篇
  1982年   752篇
  1979年   1179篇
  1978年   891篇
  1977年   843篇
  1976年   804篇
  1975年   834篇
  1974年   1034篇
  1973年   1072篇
  1972年   1022篇
  1971年   954篇
  1970年   932篇
  1969年   900篇
  1968年   754篇
  1967年   844篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
A 14-year-old domestic shorthaired cat was presented because of swelling of the digits and lameness. A solitary lung mass was observed on thoracic radiographs. Clinical and pathological evaluation confirmed a primary pulmonary squamous cell carcinoma metastatic to a single digit on each foot. Other metastatic lesions were present in the left popliteal lymph node and in the left iliac vein.  相似文献   
92.
The influences of pelleting and beta-glucanase supplementation on the digestibility of dietary components in a barley-based diet were investigated in pigs fitted with cannulas in the terminal ileum. The diet contained 49.0% starch, 18.9% crude protein and 14.8% dietary fiber, with arabinoxylans (4.9%), mixed-linked beta-glucans (3.4%) and cellulose (3.3%) as the main fiber components. Pelleting increased mixed-linked beta-glucan solubility from 45 to 62%. Neither treatment influenced the ileal or fecal apparent digestibilities of dry matter (64 and 80%, respectively), energy (62 and 79%), crude protein (53 and 75%), crude fat (26 and 27%) or dietary fiber (58 and 72%). However, pelleting increased (P less than .01) the pre-ileal apparent digestibility of starch from 91.5 to 95.3% and decreased (P less than .03) that of ash from -10 to -23%, while increasing (P less than .005) the fecal apparent digestibility of starch from 98.6 to 99.7%. The solubility of mixed-linked beta-glucans in ileal digesta was lower (P less than .001) in pelleted (26%) than in unpelleted (58%) diets. beta-glucanase supplementation also increased (P less than .05) the ileal apparent digestibility of starch, from 92.6 to 94.3%, and of mixed-linked beta-glucans, from 95.7 to 97.1%. Significant between-pig differences in the apparent digestibility of dietary components were observed. In conclusion, treatments that disrupt the endosperm cell walls in barley can increase the proportion of the diet digested prior to the large intestine.  相似文献   
93.
The spontaneous EEG and somatosensory evoked potentials (SEPs) were examined in chickens before and after electrical stunning using a waterbath stunner. Fifty-four per cent of the birds became epileptic and lost their SEPs, and 17% were non-epileptic and appeared to retain their SEPs. It was concluded that there was a reasonably close association between the presence of epileptiform activity in the EEG and the absence of SEPs following electrical stunning, but that the absence of SEPs could be preferred as an indicator of an effective stun on conceptual grounds.  相似文献   
94.
95.
Blood samples from 331 greyhounds in the Hunter Valley and nearby coastal areas of New South Wales were examined for microfilariae using a filtration technique. Species were identified by histochemical staining; 10.9% of the greyhounds were infected with Dirofilaria immitis and 3.6% with Dipetalonema reconditum. The prevalence of infection of both species was significantly greater in summer than in winter (p = less than 0.05). Infection with D. immitis was correlated with differences in age, sex, bodyweight and coat colour, and a reported lack of stamina and the presence of a cough. No significant association was found. Diethylcarbamazine citrate was used for prophylaxis in 8.8% of all the greyhounds examined.  相似文献   
96.
Three commonly used keratin monoclonal antibodies (MAB)--AE1:AE3, CAM 5.2, and MAK-6--were compared with routinely used cytokeratin antibody. The expression of these antibodies was analyzed in several tissues obtained from clinically normal dogs and in a variety of neoplasms from dogs. Using appropriate enzymatic digestion, paraffin-embedded tissues processed in routine manner retained their typical keratin expression. Differentiated and poorly differentiated epithelial neoplasms, lymphomas, and melanomas were studied by use of the avidin-biotin-peroxidase technique. All 4 of the aforementioned antibodies had similar staining profiles. Of 3 anaplastic carcinomas, 2 had positive reaction to all 4 antibodies. All lymphomas, plasma cell tumors, and amelanotic melanomas had negative reaction to MAK-6, CAM 5.2, AE1:AE3, and cytokeratin MAB. Three basal cell epitheliomas had positive reaction to all 4 antibodies, whereas 1 basal cell tumor with a solid pattern had negative staining reaction. Two carcinoids had negative reaction to all markers and 1 of 2 malignant chemodectomas and 1 transitional cell carcinoma had staining reaction to only AE1:AE3 MAB. Comparing the 4 antibodies, use of AE1:AE3 MAB produced the strongest staining intensity followed by cytokeratin, MAK-6, and CAM 5.2 MAB. All 4 antibodies had low background staining. In conclusion, AE1:AE3 and MAK-6 MAB are as useful as cytokeratin MAB for identification of poorly differentiated epithelial neoplasms in dogs and cats.  相似文献   
97.
Uptake, transfer to rough endoplasmic reticulum, and intracellular growth of Brucella abortus were studied in Vero cells treated with endocytic and metabolic inhibitors. Infection of Vero cells was suppressed when inhibitors of energy metabolism (iodoacetate, dinitrophenol), receptor-mediated endocytosis (monodansylcadaverine, amantadine, methylamine), or endosomal acidification (chloroquine, ammonium chloride, monensin) were added to the inoculum. Inhibition was not observed when these drugs were added after the inoculation period. Infection of Vero cells by B abortus was inhibited by dibutyryl-cyclic adenosine monophosphate and Vibrio cholerae enterotoxin, but was stimulated by dibutyryl-cyclic guanosine monophosphate and escherichia coli heat-stable enterotoxin a. Uptake of B abortus by Vero cells was not prevented by colchicine, but was abolished by cytochalasin B. Uptake of heat-killed B abortus and noninvasive E coli was similar to that of viable brucellae. Intracellular growth of B abortus was not affected by cycloheximide. Results indicate that: B abortus may be internalized by a receptor-mediated phagocytic process; transfer of B abortus from phagosomes to rough endoplasmic reticulum may require endosomal acidification; and replication of B abortus within the rough endoplasmic reticulum may not depend on protein synthesis by the host cell.  相似文献   
98.
Twenty-five horses admitted for minor orthopaedic or soft tissue surgery were anaesthetised with detomidine, ketamine and halothane. Heart rate, arterial blood pressure, respiratory rate, tidal volume, minute volume, blood gases and occlusion pressures were measured before and for 30 mins after intravenous (iv) injection of saline, butorphanol 0.05 mg/kg bodyweight (bwt) or morphine 0.02 or 0.05 mg/kg bwt. Drug or saline treatment induced no significant changes from pre-treatment values within a group for arterial blood pressure, heart rate, respiratory rate, arterial carbon dioxide tension, arterial oxygen tension and occlusion pressure. In conclusion, both morphine and butorphanol at the stated doses cause no adverse effects on the cardiovascular and respiratory systems of anaesthetised horses.  相似文献   
99.
The behavioural and sedative effects of intravenous (iv) romifidine (40 and 80 μg/kg bodyweight [bwt]) alone or in combination with iv butorphanol (50 μg/kg bwt) were investigated in four ponies and one Thoroughbred horse. Apparent sedation, as judged by the lowering of the head, and by the response to imposed touch, visual and sound stimuli was assessed. The combination with butorphanol reduced the animals' response to imposed stimuli when compared with the effect of the same dose of romifidine alone. Following the administration of romifidine/butorphanol combinations muzzle tremor was noted and some animals attempted to walk forward. In a separate series, the cardiopulmonary effects of iv romifidine (80 μg/kg bwt) alone, or in combination with butorphanol (50 μg/kg bwt) were investigated. Romifidine and the romifidine/butorphanol combination caused similar cardiovascular changes, these being bradycardia with heart block, and hypertension followed by hypotension. Romifidine caused a transient decrease in arterial oxygen tensions and arterial carbon dioxide tensions had increased significantly by the end of the 90 min recording period. Romifidine/butorphanol combinations produced significantly higher arterial carbon dioxide tensions during the first 15 mins after drug administration than did romifidine alone. Butorphanol at 50 μg/kg bwt iv reduced the response to imposed stimuli in horses sedated with romifidine. The combination produced no cardiovascular changes beyond those induced by romifidine alone, but did increase the degree of respiratory depression.  相似文献   
100.
Modern biotechnology promises a number of new applications in animal breeding and production. Although conventional pig breeding has achieved a high level of efficiency and productivity numerous problems have been encountered with animal health and the loss of meat quality. Selection based on phenotypic performance data of individual animals does not take into account the importance of specific genes and their relevance within a complex regulatory system. In most cases it is therefore difficult to trace back the genetic origins of clinically important disorders. The application of genetic engineering techniques in pig production will facilitate diagnosis, improvement of productivity, and animal health by allowing direct genetic manipulation. Attention must be focussed on the physical and genetic analysis of the procine genome. The isolation and characterisation of genes, DNA-markers, polymorphic DNA-fragments, and their chromosomal assignment will be important prerequisites and tools for the elucidation of genetic disorders. Especially the detection of heterozygous carriers of recessive disorders and their elimination from the breeding stock will increase selection accuracy and decrease the generation intervals. But also the rapid and simple detection of infectious diseases, which is sometimes difficult if not impossible at present, will improve animal health and welfare. Although the production of transgenic animals either by DNA-microinjection into zygotes or the use of embryonal stem cells manipulated in vitro is less straightforward than DNA-based diagnosis it will play an important role in the direct manipulation of the porcine genome and genes. Breeding programmes including the use of transgenic livestock have already been developed. There is no doubt that genetic engineering has reached a degree of practical feasibility, allowing it to play an important role in pig breeding in particular and animal production in general.  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