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   84497篇
  免费   4822篇
  国内免费   58篇
林业   2925篇
农学   2311篇
基础科学   567篇
  9325篇
综合类   14975篇
农作物   3104篇
水产渔业   3931篇
畜牧兽医   46251篇
园艺   891篇
植物保护   5097篇
  2018年   1045篇
  2017年   1192篇
  2016年   1104篇
  2015年   956篇
  2014年   1202篇
  2013年   3102篇
  2012年   2179篇
  2011年   2743篇
  2010年   1681篇
  2009年   1780篇
  2008年   2629篇
  2007年   2447篇
  2006年   2436篇
  2005年   2172篇
  2004年   2120篇
  2003年   2111篇
  2002年   1996篇
  2001年   2724篇
  2000年   2822篇
  1999年   2145篇
  1998年   823篇
  1997年   829篇
  1996年   812篇
  1995年   1022篇
  1994年   895篇
  1993年   847篇
  1992年   1942篇
  1991年   2099篇
  1990年   1930篇
  1989年   1944篇
  1988年   1846篇
  1987年   1941篇
  1986年   1986篇
  1985年   1886篇
  1984年   1499篇
  1983年   1311篇
  1982年   884篇
  1979年   1377篇
  1978年   1127篇
  1977年   987篇
  1976年   939篇
  1975年   994篇
  1974年   1283篇
  1973年   1308篇
  1972年   1242篇
  1971年   1156篇
  1970年   1097篇
  1969年   980篇
  1968年   835篇
  1967年   874篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
211.
Isolation of Haemophilus somnus from bovine milk   总被引:1,自引:0,他引:1  
  相似文献   
212.
Ketoconazole therapy in a dog with systemic cryptococcosis   总被引:1,自引:0,他引:1  
A 2-year-old dog had bilateral chorioretinitis and a cough. Systemic cryptococcosis was diagnosed by evaluating a trans-tracheal aspirate and a cryptococcal latex-particle agglutination antigen titer. Clinical remission was achieved with ketoconazole administration, an imidazole antifungal agent. Serial antigen titers were used to monitor treatment, which was continued for 12 months. Ketoconazole therapy was well tolerated by the dog.  相似文献   
213.
Membraneous phospholipids of subcellular structures were determined from the musculature of German Landrace pigs of the GDR, following exposure to halothane. Mating variants A (H+ male X H+ female), B (H+ male X H- female), and C (H- male X H+ female) were used for positive responders (MHS), while variants B, C, and D (H- male X H- female) were used for negative responders (MHN). Four phospholipid fractions were recorded from the muscle samples for mitochondria and microsomes (according to SR section). Differences between the MHS and MHN groups for the above fractions and without consideration of mating variants and genotype were not observed, although unambiguous responses were exhibited by all animals, either positive or negative to halothan. Significant differences with regard to the above phospholipid fractions were recordable only for variant A (MHS group) as compared to D (MHN), in other words, for the homozygous genotypes, once the above results had been rearranged within MHS and MHN along with different mating variants and genotypes. However, no unambiguous results were obtainable for the heterozygous genotypes of mating variants B and C. Possible underlying reasons are discussed in some detail. The results obtained from mating variants A and D are likely to confirm earlier findings and seem to suggest that the sarcoplasmic reticulum is the primary site of origin of susceptibility to halothane or malignant hyperthermia.  相似文献   
214.
The laminar epidermis (epidermis parietis) of hooves from 14 clinically normal horses, 6 months to 15 years old, was examined by light and electron microscopy and immunofluorescence to measure the contributions of this region to the formation of the hoof wall. By their progressive keratinization to form primary epidermal laminae, the secondary epidermal laminae ultimately contributed about 20% of the thickness of the hoof wall (as revealed in the white line [zona alba]). The keratinized, primary epidermal laminae were developed to a height of 4 mm during their proximodistal-course, much of this obscured because of their basal portion being embedded in the cap horn epidermis. From evaluation of structural changes accompanying keratinogenesis in the cell and determination of the contribution of the laminar epidermis to the formation of laminar horn, cap horn, connecting horn, terminal horn, and the white line, we concluded that the sterile bed concept of a nongerminative role for the secondary epidermal laminae is no longer tenable.  相似文献   
215.
An ELISA was developed to detect circulating antigens of Toxoplasma gondii in the serum of cats. For the experiment, toxoplasmosis was induced in a group of cats by oral administration of bradyzoites. An ELISA that detects anti-Toxoplasma IgG, an ELISA to detect circulating antigens, and fecal examinations were performed on samples from each cat for 1 year after inoculation. When coupled with IgG-class antibody measurement, antigen detection can aid in the diagnosis of some cases of subclinical feline toxoplasmosis.  相似文献   
216.
1. One hundred and twenty 16-week-old, single combed pullets of three strains were fed on a diet containing 160 g protein/kg with or without 50 g clinoptilolite/kg in a trial with 20 hens per treatment. Sterile river sand replaced clinoptilolite in the control diet in order to keep the diets isonergetic. 2. The hens were individually caged in a naturally-ventilated laying house and fed on one of the two diets for ten 28-d periods. 3. No significant dietary effects between treatments were observed with respect to body weight, age at first egg, egg weight, Haugh scores or food intake/hen. 4. Significant dietary effects in favour of clinoptilolite feeding were noticed with the number of eggs laid per hen, shell thickness, efficiency of food utilisation, droppings moisture content and mortality. 5. Significant differences between strains were observed with respect to all measurements taken except food intake/hen d.  相似文献   
217.
Biomicroscopy of the tear film: the tear film of the pekingese dog   总被引:1,自引:0,他引:1  
Polarised light biomicroscopy was used to examine the normal pre-corneal tear film in 21 eyes of 12 pekingese dogs. The purpose of the study was to examine the influence of excessive exophthalmos on the pre-corneal tear film in the dog. The majority of the animals were found to have high levels of ocular surface contamination by particulate material and plaques of viscous mucus. Other abnormalities included surface lipid with an abnormal granular (three dogs) or 'curdled' (two dogs) appearance; excessive thinning of the lipid layer of the tear film; and the presence of dark globular structures in two dogs, which were presumed to be abnormal meibomian lipid. Break up of the tear film was observed in one dog. Grossly, a thread of viscous mucus was frequently observed along the margin of the lower eyelid. It is postulated that this thread forms because of the excessively exophthalmic conformation of the breed, which prevents the normal access of effete mucus and entrapped debris to the lower conjunctival fornix. The combination of the above factors in the pekingese is suggested as the mechanism whereby the tear film has a reduced stability, thus enhancing the risk from factors more usually considered to initiate corneal ulceration in the breed. The possible adverse effects of lid splitting for the mass removal of distichiae in exophthalmic dogs is discussed.  相似文献   
218.
Chicken anemia agent (CAA) was isolated from broiler chickens in Texas with a blue wing or anemia dermatitis-like syndrome. Specific-pathogen-free chicks inoculated with field material developed anemia, and CAA was isolated in MDCC-MSB1 cells from bone marrow and lymphoid tissue from inoculated chicks. One isolate, designated EF88/78/276, was further characterized. Infectivity of EF88/78/276 was resistant to treatment with chloroform and with heat at 70 C for 5 minutes. EF88/78/276 was indistinguishable from the Cux-1 and Gifu-1 isolates of CAA by cross-neutralization tests. Almost all 1-day-old susceptible chicks inoculated intramuscularly with EF88/78/276 developed anemia, but contact-infected chicks did not. Antibody to CAA was detected in broiler breeder flocks from Texas, the Delmarva peninsula, and Alabama.  相似文献   
219.
Recently we reported elimination of radioactivity from [14C]heptachlor from body stores of lactating ovines, mainly into excreta rather than milk, contrasting sharply with bovines. To further assess heptachlor metabolism and clearance by ovines, 12 fine-wool wether lambs (41 +/- 3 kg) housed in metabolism stalls were fed pelleted alfalfa hay (96%) plus molasses (3%) ad libitum and were dosed i.p. once with [14C]heptachlor (1.643 mg/kg body wt; sp. act. = .89 microCi/mg). Feces and urine were collected separately and quantitatively. Light mineral oil was mixed with feed (5 g/100 g) of six lambs and trans-stilbene oxide, an inducer of biotransformational enzymes, was administered i.p. (4 g/hd initially; 2 g/hd daily thereafter) through 20 d to three lambs given each mineral oil treatment, in 2 x 2 factorial arrangement. Feces, urine, blood, bile and body tissues were assayed for total 14C activity. Radioactivity (heptachlor and [or] metabolites) eliminated into excreta during 21 d amounted to 34 to 36% of dose administered, of which 67% appeared in urine and 33% in feces. Biological half-time for elimination into excreta was 11.3 d [Kel = -.061/d], similar to 11.7 d we reported for lactating ewes. Clearance from blood had T1/2 = 14 d. Neither mineral oil nor trans-stilbene oxide altered rate or route of 14C activity excreted or concentrations of 14C activity in blood. Results confirmed that ovines eliminate heptachlor much more rapidly than bovines.  相似文献   
220.
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