全文获取类型
收费全文 | 5852篇 |
免费 | 400篇 |
国内免费 | 1559篇 |
出版年
2024年 | 5篇 |
2023年 | 84篇 |
2022年 | 112篇 |
2021年 | 152篇 |
2020年 | 146篇 |
2019年 | 271篇 |
2018年 | 235篇 |
2017年 | 221篇 |
2016年 | 209篇 |
2015年 | 270篇 |
2014年 | 309篇 |
2013年 | 414篇 |
2012年 | 416篇 |
2011年 | 397篇 |
2010年 | 273篇 |
2009年 | 392篇 |
2008年 | 390篇 |
2007年 | 415篇 |
2006年 | 384篇 |
2005年 | 354篇 |
2004年 | 308篇 |
2003年 | 307篇 |
2002年 | 305篇 |
2001年 | 205篇 |
2000年 | 204篇 |
1999年 | 178篇 |
1998年 | 121篇 |
1997年 | 77篇 |
1996年 | 108篇 |
1995年 | 131篇 |
1994年 | 82篇 |
1993年 | 64篇 |
1992年 | 57篇 |
1991年 | 43篇 |
1990年 | 31篇 |
1989年 | 25篇 |
1988年 | 21篇 |
1987年 | 23篇 |
1986年 | 14篇 |
1985年 | 10篇 |
1984年 | 14篇 |
1983年 | 10篇 |
1982年 | 14篇 |
1981年 | 4篇 |
1980年 | 1篇 |
1979年 | 3篇 |
1978年 | 1篇 |
1958年 | 1篇 |
排序方式: 共有7811条查询结果,搜索用时 17 毫秒
51.
52.
海菜花(水鳖科)-新变种-嵩明海菜花 总被引:1,自引:0,他引:1
报道了海菜花-新变种-嵩明海菜花(Ottelia acuminata var.songmingensis Z.T.Jiang,H.Li et Z.L.Dao)。该变种与原变种的区别在于叶片带状厚纸质,不透明,叶尖钝圆或具短尖。 相似文献
53.
The immature fruits of domesticated Luffa acutangula (L.) Roxb. are a common vegetable in Asia and India. To learn more about
traditional cultivars, accessions were collected from southern Yunnan Province of China, northern Laos, and southeastern Nepal,
and assessed for various parameters of genetic diversity. The size and shape of the fruits and seeds varied considerably.
A form that we found cultivated only in Nepal bore clusters of small fruits that are produced by hermaphrodite flowers. Plants
produced male flowers first, and the first node to bear flowers varied from the second to the twenty-seventh. Twenty-nine
allozyme loci were assayed. Within L. acutangula one allozyme locus was polymorphic. Luffa acutangula andL. aegyptiaca are fixed for different alleles at nine loci, indicating that they are completely reproductively isolated from each other. 相似文献
54.
Jin Xiaohua 《Brittonia》2005,57(3):255-257
Bulbophyllum wuzhishanensis, a new species from Hainan, China, is described and illustrated. The new species is probably related toBulbophyllum ledungense, but differs from it by having a long inflorescence, a column without stelids, and a longer lip. 相似文献
55.
Additional material of Todites (Osmundaceae) from the Lower Jurassic Xiangshan Group in Jiangsu and Anhui Provinces, Eastern China is investigated. Five species of Todites are described based on collections (including sterile and fertile pinnae) from eight localities along the Yangtze River, including Todites denticulatus (Brongniart) Krasser, Todites cf. goeppertianus (Muenster) Krasser, Todites nanjingensis sp. nov., Todites princeps (Presl) Gothan and Todites sp. Material of T. denticulatus and T. nanjingensis sp. nov. contains further data of the fertile pinnae. The stratigraphical ranges and the geographical distribution of the genus Todites in China are discussed and reviewed. Available data show that Todites mostly occurs in the Late Triassic to Middle Jurassic of China. The genus was widely distributed in both the Northern and Southern Floristic Provinces of China, and especially abundant and diverse in the Southern Floristic Province. 相似文献
56.
The question of cosmopolitanism in the deep-sea ostracod fauna: the example of the genus Pedicythere
E. I. Schornikov 《Hydrobiologia》2005,538(1-3):193-215
Deep-sea Pedicythere species which had been earlier considered as pan-abyssal in distribution are shown to be composite species including similar,
but separate species in the Pacific, Indian and Atlantic oceans. Morphology and distribution of Pedicythere are analysed. A key to well-described Cenozoic species and forms in open nomenclature which are referred to Pedicythere is presented, together with an annotated checklist of species. Five new species of Pedicythere are described from the South China Sea: P. hirundo sp. nov., P. gibbera sp. nov., P. dentata sp. nov., P. arator sp. nov. and P. nivea sp. nov. 相似文献
57.
我国北方植被指数对土壤湿度的敏感性分析 总被引:7,自引:0,他引:7
土壤湿度对植被指数起着重要的作用。利用NOAA-AVHRR数据中的植被指数(NDVI)和我国气象台站所监测的土壤湿度数据,对我国北方地区的NDVI与土壤湿度的关系进行了研究。结果表明,近18年来,北方地区土壤湿度不同区域其变化趋势存在差异,西北地区土壤湿度在增加,而华北和东北地区土壤湿度在下降。NDVI对土壤湿度的响应也存在着明显的区域差异,我国西北地区植被对土壤湿度的敏感性最强,其次是华北地区,敏感性弱的是东北地区;对于不同层次的土壤湿度,也表现为同样的区域特点。但随着土壤深度的增加,敏感性减弱。这种敏感性也表现在不同季节变化上,春季华北地区土壤湿度对植被指数影响较大,其次是西北和东北地区,夏季和秋季北方地区土壤湿度与植被指数都有较好的相关性,以西北地区的相关系数最大,而冬季北方地区植被指数对土壤湿度都不敏感。 相似文献
58.
59.
J. Cheng T. J. Bull P. Dalton S. Cen C. Finlayson J. Hermon-Taylor 《World journal of microbiology & biotechnology》2005,21(6-7):1175-1179
Summary Mycobacterium avium subspecies paratuberculosis infection in domestic livestock is widespread in many countries throughout the world. Studies in Europe and the USA show
that M. avium subspecies paratuberculosis can be cultured from retail pasteurized cow’s milk and that these organisms are being transmitted to humans by this route.
Most people with chronic inflammation of the intestine of the Crohn’s disease type are infected with these chronic enteric
pathogens. The production and consumption of cow’s milk has increased in China and so also has the incidence of Crohn’s disease.
The present preliminary investigation was carried out to determine whether M. avium subspecies paratuberculosis is present in the intestinal tissues of Chinese patients with Crohn’s disease who have never left China. Archival paraffin-embedded
surgical pathology blocks from patients having surgery for Crohn’s disease (CD) or for cancer (nIBD) in China were studied.
M. avium subspecies paratuberculosis was detected by nested IS900 PCR with Southern blotting and amplicon sequencing. The intestinal tissues of 9 of 13 (69.2%) CD patients and 2 of 14 (14.3%)
nIBD patients were IS900 PCR positive (P = 0.0063; odds ratio = 13.5). These initial studies suggest that people in China are exposed to M. avium subspecies paratuberculosis and that as in other countries, the infection is significantly associated with Crohn’s disease. M. avium subspecies paratuberculosis in dairy herds and retail milk in China needs to be investigated. 相似文献
60.
在编写《广东植物志》爵床科的过程中,我们采用广义爵床属Justicia的概念,因此有部分种类的名称需要重新组合.提出了爵床属4个新名称:矮爵床J.demissa N.H.Xia&Y.F.Deng,海南爵床J.hainanensis(C.Y.Wu&H.S.Lo)N.H.Xia&Y.F.Deng,线叶爵床J.neolinearifoliaN.H.Xia&Y.F.Deng和两广线叶爵床J.neolinearifolia N.H.Xia&Y.F.Deng subsp.liangkwangensis(H.S.Lo)N.H.Xia&Y.F.Deng. 相似文献