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981.
S. R. Schmolke K. Broeg S. Zander V. Bissinger P. D. Hansen N. Kress B. Herut E. Jantzen G. Krüner A. Sturm W. Körting H. von Westernhagen 《Helgoland Marine Research》1999,53(3-4):257-266
A comprehensive database, containing biological and chemical information, collected in the framework of the bilateral interdisciplinary
MARS project (”biological indicators of natural and man-made changes in marine and coastal waters”) during the years 1995–1997
in the coastal environment of the North Sea, was subjected to a multivariate statistical evaluation. The MARS project was
designated to combine a variety of approaches and to develop a set of methods for the employment of biological indicators
in pollution monitoring and environmental quality assessment. In total, nine ship cruises to four coastal sampling sites were
conducted; 765 fish and 384 mussel samples were analysed for biological and chemical parameters. Additional information on
the chemical background at the sampling sites was derived from sediment samples, collected at each of the four sampling sites.
Based on the available chemical data in sediments and black mussel (Mytilus edulis) a pollution gradient between the selected sites, was established. The chemical body burden of flounder (Platichthys flesus) from these sites, though, did not reflect this gradient equally clear. In contrast, the biological information derived from
measurements in fish samples displayed significant a regional as well as a temporal pattern. A multivariate bioindicator data
matrix was evaluated employing a factor analysis model to identify relations between selected biological indicators, and to
improve the understanding of a regional and temporal component in the parameter response. In a second approach, applying the
k-means algorithm on the data matrix, two significantly different clusters of samples, characterised by the current health
status of the fish, were extracted. Using this classification a temporal, and in the second order, a less pronounced spatial
effect was evident. In particular, during July 1996, a clear sign of deteriorating environmental conditions was extracted
from the biological data matrix.
Received: 20 June 1999 / Received in revised form: 8 November 1999 / Accepted: 8 November 1999 相似文献
982.
Christopher Nadolny 《Austral ecology》1999,24(3):258-269
The capacity of seedlings to survive for extended periods beneath intact forest increases the likelihood of regeneration of many species of canopy trees in rainforests. I studied the demographics of Argyrodendron actinophyllum (F.M.Bail.) H.L.Edlin seedlings in a subtropical rainforest in northern New South Wales. A mast seeding of A. actinophyllum was observed and subsequent survival of seedlings monitored over a four year period. Densities of seedlings that emerged correlated with seedfall, while seedfall depended on the size and distance to the surrounding trees. Mortality of seedlings showed density-dependence at higher seedling densities (above about 100 seedlings m?2), apparently in response to browsing pressure that varied with the density of seedlings. Seedlings that were protected from vertebrates by exclosure cages had lower mortality rates than unprotected seedlings and showed no density response. Glasshouse experiments showed seedling growth was reduced by defoliation, light intensity and initial seed weight, and that seedlings could not persist at light intensities below about 1% ambient, which occur in darker patches on the forest floor. Possible mechanisms whereby the observed spatial and temporal patterns of seedling recruitment could reduce the likelihood of the species becoming more common relative to other tree species in the forest are discussed. 相似文献
983.
大熊猫与黑熊显带染色体的比较研究 总被引:3,自引:0,他引:3
以体外培养的大熊猫(Ailuropodamelanoleuca)与黑熊(Selenarctosthibetanus)外周血淋巴细胞为实验材料,应用BrdU复制带显示技术,研究了大熊猫和黑熊染色体晚复制带带型。通过对大熊猫与黑熊显带染色体带型的比较,发现黑熊部分具端着丝粒的染色体与大熊猫部分具中,亚中,或亚端着丝粒的染色体的整个短臂或整个长臂有明显的带型相似性,在黑熊具中,亚中着丝粒染色体中,仅33 相似文献
984.
Toshinobu Tokumoto Mika Tokumoto Keiji Seto Ryo Horiguchi Yoshitaka Nagahama Shinpei Yamada Katsutoshi Ishikawa Manfred J. Lohka 《Experimental cell research》1999,247(2):313
We have prepared polyclonal antibodies againstXenopus20S proteasomes. The antibodies cross-react with several proteins that are common to 20S and 26S proteasomes and with at least two proteins that are unique to 26S proteasomes. The antibodies were used to analyze changes in the components of proteasomes during oocyte maturation and early development ofXenopus laevis.A novel protein with a molecular weight of 48 kDa, p48, was clearly detected in immature oocytes, but was found at very low levels in mature oocytes and ovulated eggs. p48 was reduced to low levels during oocyte maturation, after maturation-promoting factor was activated. The amount of p48 in eggs remained low during early embryonic development, but increased again after the midblastula transition. These results show that at least one component of 26S proteasomes changes during oocyte maturation and early development and suggest that alterations in proteasome function may be important for the regulation of developmental events, such as the rapid cell cycles, of the early embryo. 相似文献
985.
986.
987.
The genus Swertia is one of the large genera in Gentianaceae, including 154
species, 16 series and 11 sections. It is disjunctly distributed in Europe, Asia, Africa and N.
America, but entirely absent from Oceania and S. America.
According to Takhtajan’s (1978) regionalization of the world flora, Swertia is found in
14 regions. Eastern Asiatic region with 86 species, of which 58 are local endemics, 13 series
and 9 sections, ranks the first among all the regions. The highest concentration of the taxa
and endemics in Eastern Asiatic region occurs in SW China-Himalayan area (Sikang-Yunnan
P. , W. Sichuan, W. Yunnan-Guichou Plateau of China and NE. Burma, N. Burmense P. ,
E. Himalayan P. and Khasi-Manipur P. ). In this area there are 74 species (48 endemics),
12 series, and 9 sections; thus about half species of the world total, three quarters of series
and 82% of sections occur in this small area. Besides, the taxa at different evolutionary
stages in Swertia also survive here. It is an indication that SW. China-Himalayan area is a
major distribution centre of the genus Swertia. In addition, Sudan-Zambezian Region in
Africa, with 22 species, 4 series and 2 sections, is a second distribution centre.
The primitive type of the genus Swertia is Sect. Rugosa which consists of 2 series and
23 species. It is highly centred in the mountains of SW. China (Yunnan, Sichuan, Guizhou
and SE. Xizang) where 2 series and 16 species occur. Among them 15 species of Ser. Rugosae were considered as the most primitive groups in this genus. From our study, the outgroup of Swertia is the genus Latouchea Frahch. , which is distributed in Yunnan, Sichuan,
Guizhou, Hunan, Guangdong, Guangxi and Fujian. The two groups overlap in distribution
in SW. China. According to the principle of common origin, the ancestor of two genera ap peared most probably in this overlapping area. It was inferred that SW. China Was the birth-place of the genus Swertia.
Four sections of Swertia have different disjunct distribution patterns: Sect. Ophelia is of
Tropic Asia, Africa and Madagascar disjunct distribution; sect. Swertia is of north temperate distribution; sect. Spinosisemina is in Tropical Asia (Trop. India to S. China and Philipines); sect. Platynema also is in Tropical Asia (Java, Sumatra, Himalayas to SW. China).
These disjunct patterns indicate that the Swertia floras between the continents or between
continent and islands have a connection with each other. From paleogeographical analysis,
Swertia plants dispersed to Madagascar before the Late Cretaceous, to SE. Asian Islands in
the Pleistocene, to North America in the Miocene. The distribution of Swertia in Madagascar might be later than that in Asia. Therefore the origin time of the genus Swertia was at
least not later than the Late Cretaceous, and might be back to the Mid-Cretaceous.
The genus Swertia first fully developed and differentiated, forming some taxa at different evolutionary stages (Rugosa, Swertia, Poephila, Ophelia and Platynema etc. ) in the original area, and these taxa quickly dispersed in certain directions during the Late Cretaceous-Middle Tertiary when the global climate was warm and no much change. There seem
to be three main dispersal routes from the origin area to different continents; (1) The westward route i. e. from SW. China, along the Himalayas area to Kashmir, Pakistan,
Afghanistan and Iran, and then southwestwards into Africa throuth Arabia. Four sections
(Poephila, Macranthos, Kingdon-Wardia and Ophelia) took this dispersal route. Most
species of sect. Ophelia dispersed along this route, but a few along southern route and north
ern route. Sect. Ophelia greatly differentiated in Africa and the African endemic sectionSect. Montana was derived from it. The two sections form there a second distribution center
of Swertia. (2) The southward route, i. e. towards S. India through the Himalayas, and
towards SE. Asian islands through C. and S. China, Indo-China. Along this dispersal route
sect. Platynema, Sect. Spinosisemina and a few species of Sect. Ophelia dispersed; (3) The
northward rout, i. e. northwards across N. China, C. Asia to a high latitude of Euasia,
and also through E. Asia into N. America. The following groups took this route: sect. Rugosa, sect. Swertia, sect. Frasera, sect. Heteranthos and sect. Ophelia ser. Dichotomae.
Therefore, it seems that the genus Swertia originated in SW. China and then dispersed
from there to N. and S. Asia, Africa, Europe and North America and formed the moderndistribution pattern of this genus. 相似文献
988.
采用原代培养和传代培养法, 对1头毛冠鹿的胚肺组织细胞进行观察,发现一种新的核型,其二倍体染色体数目为2n=48,核型公式为2M+2ST+42T+XX,出现1对大的末端着丝粒染色体,C-带显示该染色体与已报道的相关染色体同源,首次提出毛冠鹿B染色体多态,对其传递机制进行了探讨。
Abstract: Primary culture and subculture were adopted using lung cells of a female Elaphodus cephalophus' embryo. A new karyotype and a pair of big telocentric chromosomes were found. The diploid has 48 chromosomes, and the karyotype formula is 2M+2ST+42T+XX. C-banding analysis shows that these chromosomes are homologous with those reported relevant chromosomes. This article is the first to report the polymorphism of Elophodus cephalophus B-chromosomes and studies it's transmitted mechanism. 相似文献
989.
H. C. Gerhardt J. Schul 《Journal of comparative physiology. A, Neuroethology, sensory, neural, and behavioral physiology》1999,185(1):33-40
The selectivity of female phonotactic responses to synthetic advertisement calls was tested in choice situations. Preferences
based on differences in the linear rise-time of synthetic pulses depended on intensity and carrier frequency. When the carrier
frequency was 1.1 kHz, simulating the low-frequency peak in the advertisement call, females preferred alternatives with slower
rise-time pulses that differed by 5 ms at playback levels of 75 dB SPL and higher. A rise-time difference of 10 ms was discriminated
at 65 dB SPL. When the carrier frequency was 2.2 kHz, simulating the high-frequency peak in the call, females discriminated
a 5-ms difference in rise-time only at 85 dB SPL. Females showed no preference when the difference was 10 ms at lower playback
levels. The difference in the thresholds (about 15–20 dB) for discriminating differences in rise-time at the two carrier frequencies
was greater than the difference in behavioral thresholds for these two frequencies (about 10 dB). This result suggests that
rise-time discrimination can be mediated solely by the neural channel mainly tuned to the low-frequency peak in the call.
Females probably assess differences in rise-time by comparing the first few pulses of each call rather than by averaging over
the entire call.
Accepted: 30 March 1999 相似文献
990.