全文获取类型
收费全文 | 20690篇 |
免费 | 1745篇 |
国内免费 | 61篇 |
专业分类
22496篇 |
出版年
2022年 | 152篇 |
2021年 | 239篇 |
2020年 | 141篇 |
2019年 | 199篇 |
2018年 | 242篇 |
2017年 | 201篇 |
2016年 | 343篇 |
2015年 | 628篇 |
2014年 | 674篇 |
2013年 | 1040篇 |
2012年 | 1135篇 |
2011年 | 1171篇 |
2010年 | 717篇 |
2009年 | 682篇 |
2008年 | 1069篇 |
2007年 | 1107篇 |
2006年 | 1017篇 |
2005年 | 1019篇 |
2004年 | 950篇 |
2003年 | 936篇 |
2002年 | 908篇 |
2001年 | 224篇 |
2000年 | 183篇 |
1999年 | 262篇 |
1998年 | 265篇 |
1997年 | 194篇 |
1996年 | 208篇 |
1995年 | 182篇 |
1994年 | 198篇 |
1993年 | 166篇 |
1992年 | 179篇 |
1991年 | 168篇 |
1990年 | 145篇 |
1989年 | 156篇 |
1988年 | 172篇 |
1987年 | 158篇 |
1986年 | 147篇 |
1985年 | 183篇 |
1984年 | 199篇 |
1983年 | 189篇 |
1982年 | 205篇 |
1981年 | 239篇 |
1980年 | 207篇 |
1979年 | 163篇 |
1978年 | 191篇 |
1977年 | 169篇 |
1976年 | 141篇 |
1975年 | 146篇 |
1974年 | 164篇 |
1973年 | 161篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
George A. Collier 《Dialectical Anthropology》1994,19(1):1-44
Thatcherism's search for the enemies within; its operations across the different lines of division and identification in social life...its rooting of itself inside a particularly narrow, ethnocentric and exclusivist conception of national identity; and its constant attempts to expel symbolically one sector of society after another from the imaginary community of the nation-these are as central to Thatcherism's hegemonic project as the privatization programme or the assault on local democracy... 相似文献
92.
Attenuation of visible light by phytoplankton in a vertically structured ocean: solutions and applications 总被引:1,自引:0,他引:1
Platt Trevor; Sathyendranath Shubha; White George N. III; Ravindran P. 《Journal of plankton research》1994,16(11):1461-1487
To find the solution to problems in applied marine optics, wedo not always need to compute the submarine irradiance at alldepths; in many cases, it is sufficient to know the averageattenuation of light for finite layers of arbitrary thickness.If multiple scattering can be neglected, the average attenuationof light in a finite layer of the water column depends onlyon the vertical distribution of the attenuating substances;in open-ocean waters, the most important of these is phytoplankton.It is shown how the average attenuation of monochromatic lightin an arbitrary layer can be determined when the vertical pigmentprofile takes one of two standardized forms: a shifted Gaussianor a triangle. The choice of efficient algorithms to computethe attenuation in a layer using these models is discussed.The extension to polychromatic light involves the selectionof a function to represent the spectral distribution of thespecific absorption coefficient for phytoplankton, as determinedby observation. Chebyshev polynomial representation is shownto be convenient for applications which require the calculationof a weighted wavelength integral. An efficient procedure forthe evaluation of these integrals, Gauss-Chebyshev quadrature,is presented and evaluated. The extension to the computationof bulk properties for discrete layers is straightforward. 相似文献
93.
Garry Lindsay Allan Jim Camakaris George J. F. Legge 《Biological trace element research》1994,40(2):103-126
A scanning proton microprobe has been used for the elemental microanalysis of individual fibroblast cells. Both normal fibroblasts and fibroblasts cultured from patients with Menkes' disease, an X-linked genetic disorder known to be associated with defective copper metabolism, were examined by the probe. The cells were cultured on a thin ultra-clean nylon foil and retained on that surface for analysis. The focused high-energy proton beam was used to irradiate selected individual cells and elemental information was derived from X-ray and backscattered proton data. The sensitivity of the scanning proton microprobe to trace concentrations of heavy elements has allowed this elemental information to be used to identify individual cells as being either normal or a Menkes' mutant. The cell identification was based on the application of discriminate analysis to a data set formed from the ratios of copper to each of the macroelements present in the cell. This method of cell identification offers the promise of rapid diagnosis of Menkes' disease. 相似文献
94.
In an attempt to characterize disease producing mutations in the factor VIII gene we screened exons 4, 7, 8, 11, 12 and 16 by PCR-SSCP (polymerase chain reactionsingle strand conformation polymorphism), in 12 randomly selected haemophilia A patients. These exons were chosen because they have been reported to harbour a disproportionately high number of mutations relative to their size. Using this strategy we detected a frame-shifting 5-bp deletion (TACCT, involving nucleotides 519–523), which is predicted to result in a severely truncated factor VIII polypeptide, terminating approximately midway through the conserved A1 domain and resulting in the observed severe phenotype. We also showed that the sequence in the vicinity of the observed deletion is concordant with the modified slipped-mispairing at DNA replication model of Krawczak and Cooper. 相似文献
95.
96.
97.
This study shows for the first time that perfusion of rat or hamster brain with a cyclohexylamine-paraformaldehyde mixture makes possible the observation by autoradiography of melatonin binding sites in structurally well-preserved fixed tissues. This result is a first step in the identification of melatonin-receptor-containing cell types by cytoautoradiography. 相似文献
98.
99.
By using a large cage in the field and a system of marking, the flight activities of 36 females and 49 males of the European chafer were followed during June and July, 1954.It was found that the beetles made one to 11 flights during their life span with males averaging five flights and females 4.5. More males made eight to 11 flights than did females, and males made more flights on consecutive evenings. The average longevity of the males was found to be six days while the females lived on the average for 6.5 days.The main flight period of the European chafer lasts about one month though some beetles can be observed flying in the evenings for about two months after the main flight has ended. The populations observed in the field are composed of successive groups of beetles which emerge, fly for several days then die. These groups overlap each other so that high numbers of beetles are present in the trees each evening during the main flight period. Variations in the physical characteristics of the soil habitat could be responsible for the differences in the time of maturity of the larvae and the subsequent first-time emergence of the adults.
Zusammenfassung Im Juni und Juli 1954 wurde die Flugtätigkeit von 36 weiblichen und 49 männlichen Tieren von Amphimallon majalis (Razoumowsky) unter Zuhilfenahme eines grossen Käfigs im freien Felde und eines geeigneten Bezeichnungssystems der Tiere verfolgt.Es zeigte sich, dass die Käfer während ihrer Lebensdauer ein bis elf Flüge unternehmen und zwar betrug der Durchschnitt für männliche Tiere fünf, für weibliche 4,5 Flüge. Mehr Männchen als Weibchen flogen 8 bis 11 mal und die Männchen flogen häufiger an aufeinanderfolgenden Abenden. Für männliche Käfer war die durchschnittliche Lebensdauer 6 Tage, während die weiblichen einen Durchschnitt von 6,5 Tagen erreichten.Die Hauptflugperiode von Amphimallon majalis erstreckt sich über etwa einen Monat, obwohl man auch 2 Monate lang nach der Hauptflugzeit des abends noch einige Käfer fliegen sehen kann. Die Gesamtzahl der im Versuchsfeld beobachteten Insekten setzt sich aus auf einander folgenden Gruppen von Käfern zusammen, die nach einander ausschlüpfen, mehrere Tage fliegen und dann sterben. Diese Gruppen überschneiden sich, so dass während der Hauptflugzeit abends eine grosse Anzahl von Käfern in den Bäumen zu finden ist. Es ist sehr wohl möglich, dass Unterschiede in der physikalischen Beschaffenheit des Bodens für die Länge der Reifezeit der Larven verantwortlich sind und somit auch für den Zeitpunkt des Erstfluges der entwickelten Käfer.相似文献
100.
Strangers Abroad Series: Sir Walter Baldwin Spencer (1860–1929), Fieldwork; Franz Boas (1858–1952), The Shackles of Tradition; William Rivers (1864–1922), Everything Is Relatives; Bron-islaw Malinowski (1884–1942), Off the Verandah; Margaret Mead (1901–1978), Coming of Age; Sir Edward Evans-Pritchard (1902–1973), Strange Beliefs. 相似文献