全文获取类型
收费全文 | 14196篇 |
免费 | 1176篇 |
国内免费 | 4篇 |
专业分类
15376篇 |
出版年
2022年 | 92篇 |
2021年 | 222篇 |
2020年 | 153篇 |
2019年 | 200篇 |
2018年 | 212篇 |
2017年 | 203篇 |
2016年 | 339篇 |
2015年 | 507篇 |
2014年 | 653篇 |
2013年 | 788篇 |
2012年 | 952篇 |
2011年 | 993篇 |
2010年 | 603篇 |
2009年 | 593篇 |
2008年 | 763篇 |
2007年 | 802篇 |
2006年 | 770篇 |
2005年 | 711篇 |
2004年 | 682篇 |
2003年 | 660篇 |
2002年 | 639篇 |
2001年 | 210篇 |
2000年 | 147篇 |
1999年 | 187篇 |
1998年 | 164篇 |
1997年 | 138篇 |
1996年 | 124篇 |
1995年 | 134篇 |
1994年 | 97篇 |
1993年 | 136篇 |
1992年 | 133篇 |
1991年 | 104篇 |
1990年 | 128篇 |
1989年 | 105篇 |
1988年 | 89篇 |
1987年 | 93篇 |
1986年 | 79篇 |
1985年 | 99篇 |
1984年 | 115篇 |
1983年 | 96篇 |
1982年 | 133篇 |
1981年 | 102篇 |
1980年 | 84篇 |
1979年 | 76篇 |
1978年 | 83篇 |
1977年 | 66篇 |
1976年 | 59篇 |
1975年 | 54篇 |
1974年 | 78篇 |
1973年 | 58篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
61.
Ian Bedford 《The Australian journal of anthropology》1996,7(2):104-120
The criteria invoked in the definition of national identity are commonly derived from contexts other than those of the nation-state itself—most notably those of territoriality, language/culture, kinship/descent and religion. It therefore follows that in seeking to understand the kind of identity or belongingness invoked in a particular instance of national ideology it is necessary to explore not only the kind of nation-state envisaged, but also those non-national forms of belonging or community from which the national ideology may itself be historically derived. In this paper I seek to develop this argument by comparing some of the principal forms of nationalism found in India, Pakistan and Central Asia. I pay particular attention to the importance of the concept qawm, which in Pakistan, Afghanistan and elsewhere in Central Asia, is used to refer to a wide variety of groups to which people owe allegiance. Such usages alert us to the important fact that the nation, as ‘imagined community’, may have its origins as a political movement among sentiments and allegiances which draw on pre-modern social arrangements and are in tension with ‘nationalist’ exclusivism. Even when the nation (as nation-state) has been secured, so-called ‘nationalist’ revivalism, while taking the nation for granted, may in fact appeal to sentiments of a different kind. 相似文献
62.
A double-antibody-sandwich, enzyme-linked immunosorbent assay was developed to detect an extracellular proteinase produced by Pseudomonas fragi. The method was capable of detecting 4 g/ml of the proteinase in spiked samples of buffer and broth and 4.2 g/ml in a broth culture of the organism. The assay detected the presence of proteinase at bacterial densities of approximately 104 cfu/ml, which develop after incubation for 15 h at 25°C in a broth medium. All assays could be completed within 7 h. This assay is of value in plotting proteolytic expression in relation to the growth cycle of Ps. fragi in broth culture and may be of value, with development, in other more complex milieux. 相似文献
63.
64.
65.
P. E. McAllister M. W. Newman J. H. Sauber W. J. Owens 《Helgoland Marine Research》1984,37(1-4):317-328
Two significant fish kills occurred in the Pamlico River estuary (North Carolina, USA), one in December 1981 and January 1982, and the other in June 1982. The first involved only the southern flounder(Paralichthys lethostigma). Histopathologic examination of morbid and moribund flounder revealed extensive sloughing and necrosis of the mucosa of the pyloric caeca and intestine, and inflammation of the submucosa of the pyloric caeca. Brain and internal organ homogenates from morbid and moribund flounder were assayed on CHSE-214 cells, and a virus was isolated. Virus titers ranged from8.4 · 102 to 6.3 · 107 TCID50 per gram of tissue. Cross-plaque neutralization assays indicated that the southern flounder virus was infectious pancreatic necrosis virus serotype Ab. Immersion challenge showed the isolate is only slightly virulent for fry of brook trout(Salvelinus fontinalis). The second fish kill involved the southern flounder and six other species: hogchoker(Trinectes maculatus), Atlantic silverside(Menidia menidia), spot(Leiostomus xanthurus), Atlantic croaker(Micropogon undulatus), silver perch(Bairdiella chrysura), and striped mullet(Mugil cephalus). Virus was isolated from southern founder, hogchoker, Atlantic silverside, and spot. Neutralization assays indicated that the four isolates were nearly identical; however, the diversity of species affected suggests that the virus might not have been the specific cause of mortality. 相似文献
66.
The distribution of immunoglobulin allotypes of the Gm and Km systems was examined in 51 patients with antinuclear antibodies (ANA), which reacted with two saline-extractable non-DNA nuclear antigens, anti-La (SS-B) and anti-RNP, which characterize certain multisystem autoimmune diseases. Forty-six percent of the 26 patients with anti-La were positive for the Km(1) allotype compared with 14% of the 35 with anti-RNP and 16% of 1204 of healthy subjects (corrected P value < 0.005). The high frequencies of the Km(1) allotype (46%), female sex (100%), and the HLA-B8, DR3 phenotype (> 90%) in patients with anti-La are indicative of a substantial inherited predisposition to the development or expression of this autoantibody. The strong association between the Km(1) allotype and the anti-La response may be due to linkage disequilibrium between genes coding for the constant region of immunoglobulin kappa light chains and genes coding for the variable regions of kappa light chains which confer antibody specificity for the special configuration of the ribonucleoprotein known as La. 相似文献
67.
A model of extinction probability, based on the general theory of island biogeography [MacArthur and Wilson, 1967], is proposed for humans on oceanic islands; extinction probability is determined by island carrying capacity, frequency and amplitude of fluctuations in resources determining carrying capacity, and the net costs of contact and exchange between population units. The model predicts that extinction probability will determine island settlement patterns within an island group resulting in nonsettlement of islands with low carrying capacities and settlement of all islands with high carrying capacities. Data examined from the Marshall Islands tend to support the model. The model is extended to initial atoll colonization patterns. Possible requirements for initial settlement are suggested.Deceased. 相似文献
68.
69.
Ian S. Zagon Patricia J. McLaughlin James E. Seely Greg W. Hoeksema Dr. Anthony E. Pegg 《Cell and tissue research》1984,235(2):371-377
Summary Ornithine decarboxylase, a key enzyme in polyamine biosynthesis and cell growth, has been localized in mouse kidney by autoradiography after administration of radiolabeled -difluoromethylornithine. This drug is an enzyme-activated irreversible inhibitor of ornithine decarboxylase and forms a covalent bond with the enzyme. It was found that ornithine decarboxylase is present in all cell types studied but that the highest content occurs in the proximal convoluted tubules followed by the distal convoluted tubules and the collecting tubules. The majority of the enzyme is located in the cytoplasm but about 10–15% is present in the nuclei (often associated with nucleolus-like components) of the cells of the proximal and distal convoluted tubules. The labeled ornithine decarboxylase was lost rapidly from both nucleus and cytoplasm of all the cell types examined, and labeling by radioactive -difluoromethylornithine was greatly reduced if the mice were pretreated for 5 h with cycloheximide to block protein synthesis. These results indicate that ornithine decarboxylase turns over rapidly in all of the cells. 相似文献
70.
The object of this study was to determine the importance of vasoconstrictor activity in the suppression of renin secretion by vasopressin. Arginine vasopressin (AVP) (0.05 and 0.1 ng/kg/min) and a nonpressor analogue of vasopressin, 1-deamino-[4-threonine, 8-D-arginine]-vasopressin (dTDAVP) (0.01 and 0.05 ng/kg/min), were infused intravenously in anesthetized hypophysectomized dogs. Neither dTDAVP nor AVP influenced arterial pressure or heart rate but both suppressed plasma renin activity. Infusion of dTDAVP at 0.01 and 0.05 ng/kg/min suppressed plasma renin activity to 86±4% (p<0.05) and 63±6% (p<0.01) of the control values respectively. Infusion of AVP at 0.05 and 0.1 ng/kg/min suppressed plasma renin activity to 60±8% (p<0.01) and 59±12% (p<0.05) of the central values respectively. dTDAVP and AVP both produced significant increases in sodium excretion. These data demonstrate that vasoconstrictor activity is not required for the effects of vasopressin on renin secretion and sodium excretion. 相似文献