全文获取类型
收费全文 | 5124篇 |
免费 | 368篇 |
国内免费 | 463篇 |
专业分类
5955篇 |
出版年
2024年 | 30篇 |
2023年 | 150篇 |
2022年 | 210篇 |
2021年 | 235篇 |
2020年 | 240篇 |
2019年 | 307篇 |
2018年 | 294篇 |
2017年 | 158篇 |
2016年 | 146篇 |
2015年 | 175篇 |
2014年 | 323篇 |
2013年 | 396篇 |
2012年 | 218篇 |
2011年 | 271篇 |
2010年 | 210篇 |
2009年 | 235篇 |
2008年 | 257篇 |
2007年 | 252篇 |
2006年 | 238篇 |
2005年 | 207篇 |
2004年 | 123篇 |
2003年 | 140篇 |
2002年 | 126篇 |
2001年 | 104篇 |
2000年 | 86篇 |
1999年 | 51篇 |
1998年 | 82篇 |
1997年 | 65篇 |
1996年 | 60篇 |
1995年 | 60篇 |
1994年 | 58篇 |
1993年 | 60篇 |
1992年 | 47篇 |
1991年 | 38篇 |
1990年 | 32篇 |
1989年 | 31篇 |
1988年 | 28篇 |
1987年 | 22篇 |
1986年 | 18篇 |
1985年 | 30篇 |
1984年 | 20篇 |
1983年 | 14篇 |
1982年 | 23篇 |
1981年 | 19篇 |
1980年 | 19篇 |
1979年 | 14篇 |
1978年 | 8篇 |
1976年 | 9篇 |
1973年 | 4篇 |
1972年 | 4篇 |
排序方式: 共有5955条查询结果,搜索用时 15 毫秒
1.
2.
Elizabeth Holt 《Dialectical Anthropology》2005,29(3-4):387-396
In this paper, I read Leïla Sebbar’s staging in her novel Shérazade: 17 ans, brune, frisée, les yeux verts of the resistance by children of North African and other immigrants in the early 1980s to the French state’s cartographic modes and documents of control. The paper will consider the many uses to which the map was put by the French state in its colonization of North Africa and particularly Algeria, and later in its attempts to control the banlieues its policies of citizenship and cartographic control yielded on the margins of Paris. In this context, I will explore the ways in which the novel’s characters, living clandestinely in a squatt, simultaneously resist, put to use, and even supercede state documents of control as they disrupt everyday life and conduct heists across the city of Paris. The paper will explore unofficial cartographies of Paris, from those afforded by the radios libres and alternative publications such as Libération and Sans Frontièrez, to oral and almost proverbial networks of knowledge criss-crossing the city of Paris, while also tracing the uses to which supplemental cartographic sketches and counterfeit identity cards are put in the pages of the novel. The paper will be in dialogue with theoretical and critical formulations of space, cartography, and state control put forward by Michel de Certeau, Henri Lefebvre, Michel Foucault, and Tom Conley. The paper will conclude with a consideration of the means and limits of resistance by the novel’s characters in the context of this body of theory and criticism. 相似文献
3.
4.
Correlative light, high-voltage electron and conventional electron microscopic methods were used to investigate digestion in two allogromiid foraminiferans, Allogromia sp., strain NF, and A. laticollaris Arnold. Microscopic observations showed that bacterial prey are phagocytosed by reticulopodia and are transported to the allogromiid cell body within blister-like phagosomes. Larger prey (algae, diatoms) are transported along the reticulopodial surface and are either stored extrathalamously or phagocytosed at the oral opening (peduncle). Studies of allogromiids optimally fixed and labeled with an extracellular-space label (colloidal thorium) showed that phagocytosed prey are completely enclosed by a plasma membrane envelope; this finding was corroborated by a serial-section three-dimensional reconstruction of the oral zone of one allogromiid. Cytochemical staining for acid phosphatase showed that lysosomes are absent from reticulopods but abundant in the cell body, particularly in the oral zone cytoplasm. We conclude that digestion in allogromiid foraminiferans is accomplished by a vacuole-based digestive apparatus and not by extracellular digestion within a lacunary system, as has been suggested in earlier studies. 相似文献
5.
R Cancedda O Capasso P Castagnola F Descalzi-Cancedda N Quarto 《Journal of cellular biochemistry》1985,28(1):7-14
In cultured chick embryo chondrocytes, type X collagen is preferentially deposited in the extracellular matrix, the ratio between type II and type X collagen being about 5 times higher in the culture medium than in the cell layer. When the newly synthesized collagens deposited in slices from the epiphyseal cartilage of 17-day-old embryo tibiae were isolated, type X collagen was always the major species. In agreement with this result the mRNA for type X collagen was the predominant mRNA species purified from the same tissue. When the total collagen (unlabeled) deposited in the epiphyseal cartilage was analyzed, it was observed that type X collagen represented only 1/15 of the type II collagen recovered in the same preparation. The possible explanations for these differences are discussed. 相似文献
6.
Stanley W. Watson Eberhard Bock Frederica W. Valois John B. Waterbury Ursula Schlosser 《Archives of microbiology》1986,144(1):1-7
A new chemolithotrophic nitrite-oxidizing bacterium, for which the name Nitrospira marina is proposed, was isolated from the Gulf of Maine. N. marina is a Gramnegative curved rod which may form spirals with 1 to 12 turns. Cells have a unique periplasmic space and lack intracytoplasmic membranes and carboxysomes. N. marina is an obligate chemolithotroph, but best growth is obtained in a mixotrophic medium. N. marina may be one of the most prevalent nitrite-oxidizing bacteria in some oceanic environments. Type strain is field with American Type Culture Collection (ATCC 43039). 相似文献
7.
David K. Chapman ers Johnsson Christina Karlsson Allan Brown David Heathcote 《Physiologia plantarum》1994,90(1):157-162
In a spaceflight experiment, autotropism by oat ( Avena sativa L.) coleoptiles following gravitropic responses was prominent in weightlessness: counter-reactions led to the straightening of the curved coleoptiles. This was not the case during clinorotation on earth. The autotropic reactions appeared to be related to the stimulus received during the stimulus period, i.e. the greater the response the greater the autotropic counter-reaction. Previous models of the gravitropic system which predicted that coleoptiles would not straighten in weightlessness are disproved. A modification to one of the models is proposed which includes the autotropic response observed in spaceflight. The nature of the counter-reactions in the absence of gravitropic stimulation is discussed. 相似文献
8.
Jorge J. Casal R. Alejandra Mella Carlos L. Ballaré Sara Maldonado 《Physiologia plantarum》1994,92(4):555-562
Etiolated Vicia faba seedlings were exposed to continuous red light to investigate whether changes in extracellular peroxidase activity were correlated in time and localization with changes in extension growth and/or lignin content in the subapical region of the epicotyl. Continuous red light: (a) increased extracellular peroxidase activity after a lag of ca 0.5 h, followed by a maximum peak after 2.5 h due to slightly acidic isoforms (pI = 6–6.5, according to isoelectrofocusing gels), a minimum after 4 h and a second maximum after 8 h due to acidic isoforms (pI=4–5), (b) increased lignin content and epicotyl resistance to bending after a lag of ca 4 h, i.e. simultaneously with changes in acidic extracellular peroxidase activity, and (c) reduced extension growth to a stable rate after a lag of ca 1 h, not coinciding with the kinetics of any of the extracellular peroxidase isoforms. These effects of continuous red light were at least partially mediated by phytochrome. Tissue printing and anatomical studies revealed red light effects on extracellular peroxidase activity and lignin content mainly in the outer cortical parenchyma. The results are consistent with the involvement of phyto-chrome-mediated effects on extracellular peroxidases (acidic isoforms) in the transduction chain leading to lignin responses to red light. 相似文献
9.
James B. Hoying Carl A. Boswell Stuart K. Williams 《In vitro cellular & developmental biology. Animal》1996,32(7):409-419
Summary During angiogenesis, the microvasculature displays both vessel remodeling and expansion under the control of both cellular
and extracellular influences. We have evaluated the role of angiogenic and angiostatic molecules on angiogenesis in anin vitro model that more appropriately duplicates the cellular and extracellular components of this process. Freshly isolated microvessel
fragments from rat adipose tissue (RFMF) were cultured within three-dimensional collagen I gels. These fragments were characterized
at the time of isolation and were composed of vessel segments observed in the microvasculature of fatin situ (i.e., arterioles, venules, and capillaries). Fragments also exhibited characteristic ablumenally associated cells including
smooth muscle cells and pericytes. Finally, fragments were encased in an extracellular matrix composed of collagen type IV
and collagen type I/III. The elongation of microvascular elements was subsequently evaluated using morphologic and immunocytochemical
techniques. The proliferation, migration, and elongation of cellular elements in microvessel fragments from rat adipose tissue
was dependent on initial fragment density, matrix density, and required serum. Inclusion of endothelial cell growth factors
to microvessel fragments from rat adipose tissue 3-D cultures resulted in the accelerated elongation of tube structures and
the expression of von Willebrand factor in cells constituting these tubes. Molecules with reported angiostatic capacity (e.g.,
transforming growth factor and hydrocortisone) inhibited vessel tube elongation.
In vitro methods have been developed to evaluate numerous mechanisms associated with angiogenesis, including endothelial cell proliferation,
migration, and phenotypic modulation. Microvascular endothelial cell fragments described in this study represent anin vitro population of cells that accurately duplicate thein vivo microcirculatory elements of fat. The proliferation of cells and elongation of microvascular elements subsequently observed
in three-dimensional cultures provides anin vitro model of angiogenesis. Microvascular formation in this system results from pre-existing microvessel fragments unlike tube
formation observed when cultured endothelial cells are placed in three-dimensional gels. This form of tube formation from
cultured endothelium is more characteristic of vasculogenesis. Thus, the formation of microvascular elements from microvessel
fragments provides the opportunity to examine the mechanisms regulating angiogenesis in anin vitro system amenable to precise experimental manipulation. 相似文献
10.
The important components of mucopolysaccharides and collagen have been analyzed in tissues of control and carcinoma of uterine cervix. Among these components hyaluronic acid and chondroitin sulphate levels were found to be increased, whereas decreased level of collagen was observed in uterine cervical carcinoma. Serum cathepsin B, D and acid and alkaline phosphatases have also been analyzed in controls and carcinoma patients before and after treatments. The activities of these enzymes have been found to increase prominently in advanced stages. Among these enzymes cathepsin B and alkaline phosphatase have exhibited remarkable increase in activity in uterine cervical carcinoma. Different modes of treatment exerted reversion of the elevated activities of these enzymes. However, combined therapy type II (radiation combined with cisplatin and cyclophosphomide) seems to be more effective in reverting the activities of these enzymes to normal levels. 相似文献