全文获取类型
收费全文 | 116638篇 |
免费 | 7130篇 |
国内免费 | 2703篇 |
专业分类
林业 | 6665篇 |
农学 | 6644篇 |
基础科学 | 2504篇 |
15333篇 | |
综合类 | 23160篇 |
农作物 | 5103篇 |
水产渔业 | 6018篇 |
畜牧兽医 | 51617篇 |
园艺 | 2325篇 |
植物保护 | 7102篇 |
出版年
2022年 | 1306篇 |
2021年 | 1876篇 |
2020年 | 1884篇 |
2019年 | 2141篇 |
2018年 | 2351篇 |
2017年 | 3032篇 |
2016年 | 2615篇 |
2015年 | 2600篇 |
2014年 | 3018篇 |
2013年 | 5290篇 |
2012年 | 4831篇 |
2011年 | 5518篇 |
2010年 | 4184篇 |
2009年 | 4068篇 |
2008年 | 4969篇 |
2007年 | 4711篇 |
2006年 | 4390篇 |
2005年 | 3722篇 |
2004年 | 3136篇 |
2003年 | 3156篇 |
2002年 | 3102篇 |
2001年 | 4059篇 |
2000年 | 3882篇 |
1999年 | 3071篇 |
1998年 | 1358篇 |
1997年 | 1415篇 |
1996年 | 1182篇 |
1995年 | 1295篇 |
1994年 | 1175篇 |
1993年 | 1085篇 |
1992年 | 2046篇 |
1991年 | 2103篇 |
1990年 | 1983篇 |
1989年 | 1983篇 |
1988年 | 1706篇 |
1987年 | 1648篇 |
1986年 | 1651篇 |
1985年 | 1538篇 |
1984年 | 1249篇 |
1983年 | 1047篇 |
1979年 | 1070篇 |
1978年 | 819篇 |
1975年 | 816篇 |
1974年 | 897篇 |
1973年 | 865篇 |
1972年 | 806篇 |
1971年 | 795篇 |
1970年 | 800篇 |
1969年 | 780篇 |
1967年 | 734篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
121.
122.
123.
L S Pelan-Mattocks B A Pesch M E Kehrli 《American journal of veterinary research》2001,62(11):1740-1744
OBJECTIVE: To develop an efficient and reliable method that accurately differentiates bovine lymphocytes from monocytes in leukograms. SAMPLE POPULATION: Blood samples from 30 healthy cows and 1 calf with bovine leukocyte adhesion deficiency. PROCEDURE: Flow cytometric analysis of intracellular complexity and CD45 expression on bovine leukocytes was compared with results for conventional light microscopy methods. Verification of leukocyte subpopulations determined by intracellular complexity and CD45 expression was conducted, using 2-color phenotypic analysis with selected monoclonal antibodies. RESULTS: The CD45 and side-scatter properties of bovine leukocytes clearly differentiated cell types, including neutrophils, eosinophils, monocytes, and lymphocytes. CONCLUSIONS AND CLINICAL RELEVANCE: This is a rapid assay that is simple to use. More importantly, it is more accurate than the conventional method that involves the use of blood slides and light microscopy, because of the ability of the assay to readily distinguish bovine monocytes and lymphocytes. Rapid preparation of samples and short analysis times allow for efficient and reliable examination of a large number of samples, and the task of viewing slides by light microscopy is eliminated. The labor-savings benefit of this procedure is most apparent in research environments that require frequent processing of batches of blood samples. 相似文献
124.
超高产水稻产量形成的气候生态特点研究 总被引:11,自引:1,他引:10
在云南和湖南异地异季种植,研究了水稻超高产形成的相应气候生态条件,结果表明:超高产水稻具有大穗、多穗、高结实率的特点.云南试区具有日较差大、日照时数多、相对湿度低,平均温度较低的气候特点,故水稻生育期较长,同化物积累多,成穗率高,灌浆强度大.湖南试区阴雨寡照是影响产量的重要因素. 相似文献
125.
126.
姜瘟病是中国生姜生产上发生较为普遍的病害,是由青枯劳尔氏菌(Ralstoniasolanacearum)引起的。此病原菌寄主范围广,可侵染44个科300多种植物。菌体短杆状,在TZC选择性培养基上培养出现白边较宽和白边较窄的两种菌落。菌系划分为5个生理小种和5个生化型,中国的姜瘟菌主要属生理小种1号,生物型属II、III、IV。此病害是一种较难防治的土传病害,在高温、高湿、雨水多、氮肥过量的情况下发生较为严重。中国植病工作者对此病害作了大量的研究工作,对中国姜瘟病的病原菌、发病规律、及防治等研究进展作一综述。 相似文献
127.
Histopathological and hematological findings in myeloid leukemia induced by a new feline leukemia virus isolate 总被引:2,自引:0,他引:2
Myeloid leukemia was induced by a new feline leukemia virus isolate FeLV-AB/GM-1 in a high proportion of cats. The latency period was short. Three to 5 weeks after infection early changes were detectable in the bone marrow, and cats developed leukemia 5 to 8 weeks after infection. The results of the present histological and cytological studies suggested that there were two stages in the development of leukemia. The first stage appeared to be equivalent to the syndrome of bone marrow dysplasia or preleukemia which, however, converted rapidly to leukemia. Cytopenia(s) were the main hematological findings in all preleukemic and leukemic cats. White blood cell counts were low or normal, but the number of leukemic and abnormal cells increased in the peripheral blood with the progression of the disease. This reliable model system lends itself to further studies to elucidate the pathogenesis of myeloproliferative disorders. 相似文献
128.
楼梯面的智能化建模问题是建筑、装饰等行业的热点问题.以AutoCAD VBA作为开发工具.给出几种楼梯面可视化参数快速建模方法,并对楼梯面的生成算法进行了探讨.使楼梯面模型的设计更具敏捷化、智能化和可交互性.开发的设计程序可作为AutoCAD命令嵌入到的AutoCAD绘图软件中.以提高用户的设计效率。 相似文献
129.
The survival of Leptosphaeria maculans , which causes phoma stem canker (blackleg), on oilseed rape residues ( Brassica napus ) in South Australia was investigated. Using a quantitative polymerase chain reaction (PCR) assay for L. maculans DNA, the pathogen was mainly detected in the upper 5 cm of the soil profile, including residues on the soil surface. As the size of organic matter particles in the soil decreased, so did the quantity of L. maculans detected in them. To obtain representative data for a field, at least 30 subsamples needed to be collected over the 0·81 ha area studied. In a survey of 49 commercial fields in South Australia, most L. maculans was detected in fields 1 year after oilseed rape had been grown, with less detected after 2 years and negligible amounts 3 years or more after cropping. The diagnostic DNA-based assay for L. maculans reduced the time and cost of studying L. maculans survival in soil and increased the sensitivity and accuracy of results compared with estimates of propagule number of colony-forming units on a semiselective medium. 相似文献
130.
At a site in Kent, perennial ryegrass (Lolium perenne) variety S24 and Italian ryegrass (L. multiflorum) variety RVP, wheat varieties Armada and Norman, and the original mixed grass ley were grown in small plots during 1982–84. Two toxic pesticides (phorate and aldicarb) were applied to half the total number of plots three times each year to eliminate soil invertebrate populations. Fertilizer was also applied to most plots. The yields of the crops, grown with and without pesticide, and the effects of the fertilizer were compared. Grass herbage yield was measured on three occasions during the summers of 1983 and 1984. Wheat grain yields were also determined in 1983. During the first year significant differences were not apparent in grass dry matter yield between pesticide-treated and non-treated plots, but significant differences were found in the second year. The perennial ryegrass was more susceptible to pest damage than the Italian ryegrass or the grass ley. Grass yields varied between cuts and in relation to variety and pesticide treatment, yields tending to be greater in untreated plots. Fertilizer treatment greatly increased grass dry matter yields, particularly with the Italian ryegrass. The effects of pesticide treatment on both wheat varieties varied although some yield enhancement was evident. Invertebrate animal populations in pesticide and fertilizer-treated plots were also assessed in autumn 1982, spring and autumn 1983 and spring 1984. In contrast to pesticide treatment, fertilizer treatment had little effect on soil invertebrate populations. Nematode populations were reduced at each sampling occasion by the pesticide treatment. Slug populations were initially unaffected but were subsequently reduced. Leatherjackets, by far the most abundant pest in both grass and wheat plots, were markedly affected by pesticides on all sampling occasions. Generally, fewer soil-dwelling dipterous larvae were recovered in spring than in autumn. Stem-boring dipterous larvae were virtually absent. 相似文献