全文获取类型
收费全文 | 452749篇 |
免费 | 46805篇 |
国内免费 | 218篇 |
专业分类
499772篇 |
出版年
2018年 | 4134篇 |
2016年 | 5470篇 |
2015年 | 7519篇 |
2014年 | 8695篇 |
2013年 | 12564篇 |
2012年 | 13957篇 |
2011年 | 14524篇 |
2010年 | 9700篇 |
2009年 | 8811篇 |
2008年 | 12594篇 |
2007年 | 13280篇 |
2006年 | 12553篇 |
2005年 | 11797篇 |
2004年 | 11914篇 |
2003年 | 11432篇 |
2002年 | 11250篇 |
2001年 | 17738篇 |
2000年 | 17728篇 |
1999年 | 14383篇 |
1998年 | 5328篇 |
1997年 | 5532篇 |
1996年 | 5259篇 |
1995年 | 4936篇 |
1994年 | 4828篇 |
1993年 | 4828篇 |
1992年 | 12483篇 |
1991年 | 12300篇 |
1990年 | 12289篇 |
1989年 | 12055篇 |
1988年 | 11339篇 |
1987年 | 10653篇 |
1986年 | 9992篇 |
1985年 | 10414篇 |
1984年 | 8608篇 |
1983年 | 7428篇 |
1982年 | 5784篇 |
1981年 | 5190篇 |
1980年 | 4836篇 |
1979年 | 8213篇 |
1978年 | 6410篇 |
1977年 | 6051篇 |
1976年 | 5800篇 |
1975年 | 6251篇 |
1974年 | 6804篇 |
1973年 | 6677篇 |
1972年 | 6204篇 |
1971年 | 5616篇 |
1970年 | 4834篇 |
1969年 | 4839篇 |
1968年 | 4512篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
A finite element based method to determine the incremental elastic material properties of planar membranes was developed and evaluated. The method is applicable to tissues that exhibit inhomogeneity, geometric and material nonlinearity, and anisotropy. Markers are placed on the tissue to form a four-node quadrilateral element. The specimen is loaded to an initial reference state, then three incremental loading sets are applied and the nodal displacements recorded. One of these loadings must include shear. These data are used to solve an over-determined system of equations for the tangent stiffness matrix. The method was first verified using analytical data. Next, data obtained from a latex rubber sheet were used to evaluate experimental procedures. Finally, experiments conducted on preconditioned rat skin revealed nonlinear orthotropic behavior. The vector norm comparing the applied and calculated nodal force vectors was used to evaluate the accuracy of the solutions. 相似文献
32.
Argon laser surgery is an effective treatment for ectasias and congenital port-wine stains; however, its use in children under the age of 13 is controversial. This paper reviews 202 children under the age of 13 who underwent argon laser treatments for congenital port-wine stains, spider angiomas, epidermal nevi, and lentigines. The clinical characteristics of port-wine stains in 170 children are discussed. Good to excellent results (moderate to complete clearing) in port-wine stains were obtained in 60 percent of patients and seemed to correlate best with lack of blanchability on pressure. Hypertrophic scarring was seen in only 7 children, all of whom had undressed wounds; no significant scarring has been seen in any subsequent child who had maintained a dressed wound postoperatively. 相似文献
33.
34.
35.
36.
37.
The frequency of cytokine-producing CD4-/CD8- mononuclear cells was assessed in patients of different age groups (29 infants, aged 1-5 years; 30 schoolchildren, aged 6-14 years, 26 adults, aged > 15 years) with acute Plasmodium falciparum malaria, from Gabon. Fifteen patients were followed up before antimalarial treatment (day 0), during parasite clearance (day 3) and after resolution of parasitemia (day 10). By using flow cytometry for intracellular detection of cytokines, a striking expansion of CD4-/CD8- cells producing the type 1 cytokines interleukin (IL)-2-/interferon (IFN)-gamma+, IL-2+/IFN-gamma+ and IL-2+/IFN-gamma- was observed in adults as compared with children. Type 2 cytokine expression (IL-4+/IFN-gamma-, IL-13+/IFN-gamma-) and type 0 cells (IL-4+/IFN-gamma+, IL-13+/IFN-gamma+) were not significantly different between the three age groups. Patients with severe malaria had a significantly increased frequency of type 2 cytokine-producing CD4-/CD8- cells. Drug-induced clearance of parasitemia was characterized by a decrease of IL-2+/IFN-gamma- and type 2 cytokine expressing CD4-/CD8- cells and by a gradual increase of IL-10+/IFN-gamma- expression. The type 1/type 2 dichotomy observed within the CD4-/CD8- cell population is likely to be of significance in the host response against P. falciparum malaria. 相似文献
38.
Binding of the cationic tetra(tributylammoniomethyl)-substituted hydroxoaluminum phthalocyanine (AlPcN4) to bilayer lipid membranes was studied by fluorescence correlation spectroscopy (FCS) and intramembrane field compensation (IFC) methods. With neutral phosphatidylcholine membranes, AlPcN4 appeared to bind more effectively than the negatively charged tetrasulfonated aluminum phthalocyanine (AlPcS4), which was attributed to the enhancement of the coordination interaction of aluminum with the phosphate moiety of phosphatidylcholine by the electric field created by positively charged groups of AlPcN4. The inhibitory effect of fluoride ions on the membrane binding of both AlPcN4 and AlPcS4 supported the essential role of aluminum-phosphate coordination in the interaction of these phthalocyanines with phospholipids. The presence of negative or positive charges on the surface of lipid membranes modulated the binding of AlPcN4 and AlPcS4 in accord with the character (attraction or repulsion) of the electrostatic interaction, thus showing the significant contribution of the latter to the phthalocyanine adsorption on lipid bilayers. The data on the photodynamic activity of AlPcN4 and AlPcS4 as measured by sensitized photoinactivation of gramicidin channels in bilayer lipid membranes correlated well with the binding data obtained by FCS and IFC techniques. The reduced photodynamic activity of AlPcN4 with neutral membranes violating this correlation was attributed to the concentration quenching of singlet excited states as proved by the data on the AlPcN4 fluorescence quenching. 相似文献
39.
40.
A putative GDP–GTP exchange factor is required for development of the excretory cell in Caenorhabditis elegans 下载免费PDF全文
Norio Suzuki Matthew Buechner Kiyoji Nishiwaki David H. Hall Hiroyuki Nakanishi Yoshimi Takai Naoki Hisamoto Kunihiro Matsumoto 《EMBO reports》2001,2(6):530-535
The Caenorhabditis elegans excretory cell extends tubular processes, called canals, along the basolateral surface of the epidermis. Mutations in the exc-5 gene cause tubulocystic defects in this canal. Ultrastructural analysis suggests that exc-5 is required for the proper placement of cytoskeletal elements at the apical epithelial surface. exc-5 encodes a protein homologous to guanine nucleotide exchange factors and contains motif architecture similar to that of FGD1, which is responsible for faciogenital dysplasia. exc-5 interacts genetically with mig-2, which encodes Rho GTPase. These results suggest that EXC-5 controls the structural organization of the excretory canal by regulating Rho family GTPase activities. 相似文献