全文获取类型
收费全文 | 9058篇 |
免费 | 378篇 |
国内免费 | 849篇 |
出版年
2023年 | 72篇 |
2022年 | 105篇 |
2021年 | 121篇 |
2020年 | 138篇 |
2019年 | 182篇 |
2018年 | 161篇 |
2017年 | 150篇 |
2016年 | 264篇 |
2015年 | 300篇 |
2014年 | 422篇 |
2013年 | 739篇 |
2012年 | 551篇 |
2011年 | 506篇 |
2010年 | 297篇 |
2009年 | 418篇 |
2008年 | 462篇 |
2007年 | 449篇 |
2006年 | 393篇 |
2005年 | 354篇 |
2004年 | 333篇 |
2003年 | 352篇 |
2002年 | 382篇 |
2001年 | 282篇 |
2000年 | 272篇 |
1999年 | 228篇 |
1998年 | 204篇 |
1997年 | 211篇 |
1996年 | 225篇 |
1995年 | 261篇 |
1994年 | 184篇 |
1993年 | 128篇 |
1992年 | 146篇 |
1991年 | 124篇 |
1990年 | 139篇 |
1989年 | 102篇 |
1988年 | 24篇 |
1987年 | 22篇 |
1986年 | 21篇 |
1985年 | 31篇 |
1984年 | 37篇 |
1983年 | 22篇 |
1982年 | 43篇 |
1981年 | 50篇 |
1980年 | 100篇 |
1979年 | 113篇 |
1978年 | 60篇 |
1977年 | 37篇 |
1976年 | 15篇 |
1974年 | 15篇 |
1973年 | 13篇 |
排序方式: 共有10000条查询结果,搜索用时 234 毫秒
1.
Abstract Two new species of water mites, Pionopsis (s.s.)longicosta sp. nov. and Pionopsis (s.s.) zhaoi sp. nov. are described in the present paper. This is the first record of the genus of the subfamily Tiphyinae in the family Pionidae from China. 相似文献
2.
Intracellular Development of Enterocytozoon, A Unique Microsporidian Found in the Intestine of AIDS Patients 总被引:2,自引:0,他引:2
Enterocytozoon was 1st described in 1985, in an AIDS patient with intestinal malabsorption and diarrhea. Since then, additional cases of infection with this organism have been observed, but only in individuals with AIDS and malabsorption. Intestinal tissue biopsies were obtained from a 45-year-old man prior to AIDS diagnosis, again nine months later and then at autopsy two months later. When the biopsies were examined electron microscopically, both sets contained the microsporidian parasite. However, the 2nd intestinal biopsy, when wasting was much more severe, contained infection in almost every small intestinal enterocyte examined. The parasite was actively developing, allowing us to detail its life cycle. The parasite is apansporoblastic, polysporous and has characteristics not previously reported in the Microsporida: (1) an electron lucent inclusion not usually seen in Microsporida is prominent and always present; (2) extremely elongated sausage-shaped nuclei occur in the proliferative phase of parasite development; (3) the polar tube development uniquely involves the production of electron dense discs, yet results in the formation of a typical spore; and (4) polar tube development occurs prior to the final division of the multi-nucleate sporont. On the basis of these characteristics, we are placing this genus in a new family, Enterocytozoonidae, n. fam. 相似文献
3.
4.
本记述锐顶天牛属一新种,即墨脱锐颚天牛Cleptometopus motuoensis sp.nov.。模式标本保存于西南农业大学植保系昆虫标本馆。 相似文献
5.
《法国昆虫学会纪事》2012,48(6):471-481
SummaryTwo French fossil Histeridae are described or revised, viz. Hister cerestensis n. sp. from the Oligocene of Céreste (Lubéron) and Plegaderus pitoni (Theobald, 1935), n. comb. from the Pliocene of Chambon Lake (Puy-de-Dôme). Morphometric data are used to compare fossil and extant taxa, with multivariate statistics. A list of the fossil Histeridae is given. 相似文献
6.
7.
8.
The Lithuanian bat fauna includes 14 species. Myotis daubentoni, Pipistrellus nathusii, Plecotus auritus and Eptesicus serotinus are the most abundant and widespread species, although recently P. auritus has disappeared from some hibernacula. There are still abundant populations of Myotis nattereri, Myotis brandti and Barbastella barbastellus in hibernacula, while their status in summer is unknown. Myotis dasycneme is probably very rare and endangered. The status of Myotis mystacinus and Nyctalus leisleri is not clear, but they are most likely very rare because very few specimens have been found. So far little is known about status of Nyctalus noctula, Pipistrellus pipistrellus, Eptesicus nilssoni and Vespertilio murinus because these species are common only during autumn bat migration along the Baltic Sea coast. Two other species, Myotis bechsteini and Rhinolophus hipposideros, have been rejected from the list of bats of Lithuania, because old references to records of these species were not reliable. From what is currently known it seems that: (i) the northern limits of distribution of B. barbastellus and E. serotinus reach the middle of Lithuania between 55°N and 56°N, which may also be the southern limit of abundance of E. nilssoni; (ii) the wintering site with the largest numbers of bats in Lithuania is the vaults of Kaunas fortress, where every year eight species are found hibernating in numbers estimated as follows: M. daubentoni 400–500, M. nattereri 200–300, M. brandti 80–100, B.barbastellus 200–300, P. auritus 40–60, M. dasycneme 15–20 and a few E. serotinus and E. nilssoni. In Lithuania nine bat species have been protected by law since 1991, as species included in the Red Data Book. Also 11 bat reserves have been designated in Kaunas fortress to protect the most important hibernation sites in Lithuania. 相似文献
9.
Juan P. Carricart-Ganivet David J. Barnes 《Journal of experimental marine biology and ecology》2007,344(1):67-72
Skeletons of massive coral colonies contain annual density bands that are revealed by X-radiography of slices cut along growth axes. These bands allow measurement of skeletal growth parameters such as annual extension rate and annual calcification rate. Such measurements have been important in understanding coral growth, in assessing environmental impacts and in recovering proxy environmental information. Measurements of coral calcification rate from annual density banding require measurements of skeletal density along tracks across skeletal slices and, until now, such density measurements have depended upon specialized and expensive equipment. Here, we describe a straightforward, inexpensive and accurate technique for measuring skeletal density from digitized images of X-radiographs of coral skeletal slices. An aragonitic step-wedge was included in each X-radiograph of a coral slice together with two aluminium bars positioned along the anode-cathode axis. Optical density was measured along tracks across the X-ray images of these different objects. The aragonite step-wedge provided a standard for converting optical density to skeletal density. The aluminium bars were used to correct for the heel effect—a variation in the intensity of the X-ray beam along the anode-cathode axis that would, otherwise, introduce large errors into measurements of skeletal density. Exposure was found to vary from X-radiographs to X-radiograph, necessitating the inclusion of the calibration standards in each X-radiograph of a coral slice. Results obtained using this technique compared well with results obtained by direct gamma densitometry of skeletal slices. 相似文献
10.
Herbert Budzikiewicz Mathias Schäfer Diana Uría Fernández Sandra Matthijs Pierre Cornelis 《Biometals》2007,20(2):135-144
Characteristic fragment ions of the various chromophores of the pyoverdin siderophore family obtained by collision activated
dissociation of the [M+2H]2+ ions are reported allowing unambiguous identification. Tandem mass spectrometrical studies revealed the existence of the
first example of a ferribactin with a succinamide side chain, and they add some information to the problem in which way a
malic acid side chain is attached to the chromophore. 相似文献