全文获取类型
收费全文 | 9612篇 |
免费 | 890篇 |
国内免费 | 614篇 |
出版年
2024年 | 19篇 |
2023年 | 163篇 |
2022年 | 131篇 |
2021年 | 278篇 |
2020年 | 345篇 |
2019年 | 360篇 |
2018年 | 306篇 |
2017年 | 315篇 |
2016年 | 342篇 |
2015年 | 406篇 |
2014年 | 466篇 |
2013年 | 745篇 |
2012年 | 434篇 |
2011年 | 425篇 |
2010年 | 333篇 |
2009年 | 438篇 |
2008年 | 472篇 |
2007年 | 433篇 |
2006年 | 447篇 |
2005年 | 404篇 |
2004年 | 339篇 |
2003年 | 365篇 |
2002年 | 343篇 |
2001年 | 284篇 |
2000年 | 235篇 |
1999年 | 199篇 |
1998年 | 206篇 |
1997年 | 211篇 |
1996年 | 148篇 |
1995年 | 159篇 |
1994年 | 130篇 |
1993年 | 141篇 |
1992年 | 110篇 |
1991年 | 99篇 |
1990年 | 91篇 |
1989年 | 106篇 |
1988年 | 78篇 |
1987年 | 70篇 |
1986年 | 71篇 |
1985年 | 58篇 |
1984年 | 70篇 |
1983年 | 47篇 |
1982年 | 55篇 |
1981年 | 52篇 |
1980年 | 45篇 |
1979年 | 42篇 |
1978年 | 24篇 |
1977年 | 21篇 |
1976年 | 18篇 |
1974年 | 12篇 |
排序方式: 共有10000条查询结果,搜索用时 62 毫秒
91.
Claudio Nicolini Andrew S. Belmont Antonietta Martelli 《Cell biochemistry and biophysics》1986,8(2):103-117
Using HeLa S-3 cells synchronized by selective detachment, in this paper we report a parallel study of nuclear morphology
and autoradiography grain patterns between middle G1 and middle S phases: Our results show two distinct [3H]-thymidine labeling patterns. The first “peripheral” labeling pattern has a characteristic nuclear size distribution, in
contrast to the heterogeneous and varying size distributions of Feulgen-stained nuclei, and apparently is characteristic of
very early S phase. The sizes of the second labeling pattern—homogeneous or inhomogeneous grain distribution throughout the
nucleus—are equal or larger than the first and vary with S phase progression. Together, the corresponding nuclear sizes of
the labeled nuclei represent the larger extreme of nuclear areas, and the labeling index closely parallels the fraction of
nuclei with areas larger than the minimum size of the labeled nuclei. These results suggest a characteristic nuclear size
(reflecting unique intranuclear DNA distribution) as a necessary, if not sufficient, requirement for S phase initiation. Parallel
experimentation with rat liver cells—synchronized in vivo by partial hepatectomy and analyzed by thin section autoradiography—confirms
the existence of a peripheral labeling pattern in both the very early part and the very late part of S phase, which reconciles
our data with previous results and points to the fact that both initiation and termination sites for DNA replication are near
the nuclear periphery. 相似文献
92.
中国10种松树的疱锈病菌锈孢子表面形态,在扫描电镜下观察并进行比铰,可归纳为两种类型:一是以单维管束松类的五针松的红松疱锈病菌(Cronartium ribicola)为代表,包括华山松和西伯利亚红松;另一是以双维管束松类的云南松疱锈病菌(C. flaccidum)为代表,包括樟子松、油松、赤松、马尾松、黄山松、思茅松等。孢子表面突起的形状及环纹层次是识别这两种锈疱子的主要特征。 相似文献
93.
94.
Dolichodorus miradvulvus n. sp. from Anubias nana Engler in Florida is described and illustrated. The female is characterized by deep grooves in the cuticle on the ventral surface just anterior and posterior to the vulva, and by transversely elongate pouches anterior and posterior to the vulva. Both sexes have a constricted area of the stylet shaft just anterior to the knobs, and on the male the intersection of the lateral field and bursa appear sclerotized. 相似文献
95.
Species of the genus Paradoxostoma Fischer are an important component of marine and estuarine ostracod faunas throughout the world. This revision of the genus in British waters deals with 17 species of which six are described as new. Each species is diagnosed and illustrated in detail, and comments are made on their ecology and distribution. The specialized mouthparts which characterize the genus are illustrated by means of the scanning electron microscope for the first time. A key to the genus is given. 相似文献
96.
It is sometimes necessary to identify eitherH. bulbosum orH. murinum on the basis of the inflorescence or seeds alone. The majority of taxonomic keys use the presence of swollen basal culms for the former against the annual habit for the latter. Confusion is due to similarities in inflorescences and spikelet morphology. Lodicules which always persist and are present beside the fruit in a mature caryopsis, and other characters such as the awns of the lemmas of the lateral spikelets enable conclusive distinction. 相似文献
97.
Evidence from morphology and anatomy (including embryology), as well as from palynology, chemistry and cytology, indicates
thatHydrastis is quite divergent from Ranunculaceae (in which the genus has been most often included) as well as from both Glaucidiaceae
and Berberidaceae. Distinctive features ofHydrastis, which demarcate it from Ranunculaceae but which are sometimes shared by Berberidaceae, are: the unique mode of origin of
the vascular supply to stamens and carpels; the micropyle being formed by both integuments; the xylem not V-shaped in cross
section; scalariform vessel perforations present; haploid chromosome number 13; pollen tectum consisting of a compound layer
of striae; leaf mesophyll not differentiated; the unique course of stem medullary bundles; D-galactose present. Its distinctive
higher haploid chromosome number, as well as its many less-specialized character states (in floral structure, leaf anatomy,
and xylem and vessel morphology), suggest thatHydrastis is a relictual primitive group which diverged early from a common ancestral stock of Ranunculaceae, Berberidaceae and probably
of Circaeasteraceae; at least some of the features shared byHydrastis and one or another of the families concerned seem to be a heritage from their common ancestor. We propose a reestablishment
of a monotypic family, Hydrastidaceae. 相似文献
98.
Switzerland is one of the few countries where high fertility rates have been reported in cattle hydatid cysts and where the cattle/dog cycle is the most important for the maintenance of Echinococcus granulosus. The developmental and morphological characteristics of E. granulosus of Swiss cattle origin were studied and compared with that of E. granulosus of domestic animal origin from Great Britain and Australia, countries where bovine hydatid cysts are usually sterile and cattle play little role in the life-cycle of the parasite. Adult E. granulosus of Swiss cattle origin differed markedly in its developmental characteristics compared to other isolates, particularly in its rate of maturation in dogs, producing eggs as early as 35 days post-infection. The morphology of E. granulosus of Swiss cattle origin was characteristic and it could be easily distinguished from other isolates of the parasite. Further, E. granulosus of Swiss cattle origin was found to closely resemble that occurring in cattle in South Africa where high fertility rates have also been reported in bovine hydatid cysts. It is concluded that a strain of E. granulosus exists which is adapted to cattle and that further studies are required to determine whether this strain warrants formal taxonomic status as the species E. ortleppi which was originally described for the parasite of South African cattle origin. 相似文献
99.
100.
JENNIFER M. EDMONDS F.L.S. 《Botanical journal of the Linnean Society. Linnean Society of London》1984,88(3):237-251
J. M. EDMONDS, 1984. Pollen morphology of Solanum L. section Solnnum . The pollen morphology of both dried and fresh, fixed material was examined using SEM. The work confirmed thc spheroidal to sub-prolate shape, the tricolporate nature and the granular surface sculpturing, typical of Solanurn pollen, but failed to demonstrate the occurrence of exine patterns which could bc of practical taxonomic use is differentiating the species belonging to the section Solanurn . Quantification of the exine sculpturing, by means of granule density counts, indicated a possible relationship between this feature and the morpho-genetic diversity of certain species. 相似文献