全文获取类型
收费全文 | 8152篇 |
免费 | 416篇 |
国内免费 | 242篇 |
出版年
2024年 | 14篇 |
2023年 | 62篇 |
2022年 | 72篇 |
2021年 | 80篇 |
2020年 | 183篇 |
2019年 | 231篇 |
2018年 | 241篇 |
2017年 | 175篇 |
2016年 | 160篇 |
2015年 | 157篇 |
2014年 | 628篇 |
2013年 | 847篇 |
2012年 | 497篇 |
2011年 | 406篇 |
2010年 | 267篇 |
2009年 | 343篇 |
2008年 | 336篇 |
2007年 | 405篇 |
2006年 | 333篇 |
2005年 | 355篇 |
2004年 | 239篇 |
2003年 | 241篇 |
2002年 | 207篇 |
2001年 | 202篇 |
2000年 | 137篇 |
1999年 | 154篇 |
1998年 | 179篇 |
1997年 | 144篇 |
1996年 | 160篇 |
1995年 | 212篇 |
1994年 | 203篇 |
1993年 | 164篇 |
1992年 | 146篇 |
1991年 | 88篇 |
1990年 | 74篇 |
1989年 | 47篇 |
1988年 | 41篇 |
1987年 | 33篇 |
1986年 | 36篇 |
1985年 | 41篇 |
1984年 | 49篇 |
1983年 | 33篇 |
1982年 | 37篇 |
1981年 | 32篇 |
1980年 | 33篇 |
1979年 | 23篇 |
1978年 | 13篇 |
1977年 | 12篇 |
1976年 | 12篇 |
1973年 | 8篇 |
排序方式: 共有8810条查询结果,搜索用时 15 毫秒
991.
992.
993.
The present study investigated the expression of the apoptosis-related genes fas-associated via death domain (FADD) and Bcl-2 in the endometrium during the window of implantation in polycystic ovary syndrome (PCOS) patients. The aim was to explore the role of cell apoptosis in endometrial receptivity during this period. The subjects were divided into experimental and control group. The experimental group comprised 12 infertile women with PCOS, and the control group comprised 12 women who were infertile because of tubal pathological factors but had normal menstrual cycles. Endometria were collected by biopsy 7d after ovulation. Six samples from each group were randomly selected and subjected to gene chip analyses. The expression of endometrial FADD and Bcl-2 was determined by immunohistochemistry, and cell apoptosis was detected by the TUNEL method. Compared with the control group, 194 differentially expressed genes were found in the PCOS group, 102 of which were upregulated and 92 were downregulated. The differentially expressed genes were divided into 15 types according to function. Among the nine genes related to cell apoptosis, five (including Bcl-2) were upregulated and four were downregulated (including FADD). Bcl-2 expression during the window of implantation in the PCOS group increased compared with the control group, showing a significant difference (P<0.05). FADD expression in the PCOS group notably decreased compared with that in the control group, which also showed a significant difference (P<0.05). Cell apoptosis analysis showed a significant difference between the average apoptotic indices in the PCOS and control groups (P<0.05). Significant differences were observed between the endometrial gene expression in the PCOS and control groups. The decrease in cell apoptosis during the window of implantation in PCOS patients may be one of the causes of the reduced endometrial receptivity. 相似文献
994.
Tomás de Las Casas Engel Esther M. Sánchez‐carnerero Ekaterina Sokolovskaya Claudio M. Gallardo‐araya Florencio Moreno JimÉnez Beatriz Lora Maroto Santiago de la Moya Cerero 《Chirality》2012,24(10):771-777
Polystyrene grafted with a chiral zinc‐complexing camphor‐derived N,N‐disubstituted hydroxyamide is proposed as a new type of functional polymer of high reusability for the development of sustainable organozinc‐catalyzed asymmetric reactions. The main goal of this new functional polymer is the ease of the hydroxyamide‐moiety preparation (cheap chiral ligand obtained straightforwardly from an enantiopure starting material coming from the chiral pool), as well as its chemical robustness when compared with other related zinc‐complexing functional groups. The latter allows the polymer to be active after multiple applications, without significant loss of its catalytic activity. This fact is exemplified by the design and preparation of a polymer functionalized with a bis(hydroxyamide) proved previously as active in the homogeneous enantioselective addition of diethylzinc to aldehydes. The result is a cheap functional polymer with a very high reusability (the enantioselectivity and chemical yield are maintained practically constant after 20 applications). Additionally, a methodology for the multicycle use of these functional polymers is presented. Chirality, 2012. © 2012 Wiley Periodicals, Inc. 相似文献
995.
Koji OtaniTetsuya Tanigawa Toshio WatanabeYuji Nadatani Mitsue SogawaHirokazu Yamagami Masatsugu ShibaKenji Watanabe Kazunari TominagaYasuhiro Fujiwara Tetsuo Arakawa 《Biochemical and biophysical research communications》2012,426(3):342-349
Helicobacter pylori (H. pylori)-induced immune responses in the gastric mucosa are skewed toward T helper (Th) 1 phenotype, which is characterized by predominant production of tumor necrosis factor (TNF)-α and interferon (IFN)-γ by helper T cells. Toll-like receptors (TLRs) play an essential role in mucosal defense against microbes through the recognition of bacterial molecules. Among the members of the TLR family, TLR9 recognizes bacterial unmethylated CpG DNA sites, and signal transduction of TLR9 induces production of a variety of cytokines, including type-I IFN (IFN-α/β). We investigated the expression and role of TLR9 in H. pylori-induced gastritis in mice. Expression of TLR9 mRNA in the gastric tissue increased after infection with H. pylori. TLR9 was mainly expressed in the macrophages, dendritic cells, and CD3+ cells in the gastric mucosa. Neutrophil infiltration and the expression levels of TNF-α and IFN-γ mRNA were higher in TLR9 knockout (KO) mice than in wild-type mice at 2 and 4 months after H. pylori inoculation. These differences in inflammatory parameters between H. pylori-infected wild-type and TLR9 KO mice disappeared 6 months after H. pylori inoculation. Expression of interleukin-4 mRNA, typical Th2 cytokine, in the gastric tissue did not differ between H. pylori-infected wild-type and TLR9 KO mice. Expression level of IFN-α/β mRNA in the TLR9 KO mice was lower than that in wild-type mice by 4 months after inoculation. Administration of IFN-α reduced H. pylori infection-induced increase in neutrophil infiltration and the expression levels of TNF-α and IFN-γ mRNA in TLR9 KO mice. Our findings suggest that TLR9 signaling plays important roles in the suppression of H. pylori-induced gastritis in the early phase via downregulation of Th1-type cytokines modulated by IFN-α. 相似文献
996.
Akihiko KomineMotoko Abe Toshiyuki SaekiTakahiro Terakawa Chiyoko UchidaTakafumi Uchida 《Biochemical and biophysical research communications》2012,426(4):468-474
Mesenchymal stem cells (MSCs) can differentiate into a variety of cell types. MSCs exist in several tissues such as the bone marrow, adipose, muscle, cartilage, and tendon. This differentiation potential makes MSCs candidates for cell-based therapeutic strategies for mesenchymal tissue injuries. MSCs can be prepared from bone marrow (BM-MSCs) and adipose (AD-MSCs); however, these MSCs exhibit senescence-associated growth arrest and display inevitable heterogeneity. We established several AD-MSC cell lines from a p53-knockout (KO) mouse. These cell lines were immortalized, but no cell lines grew anchorage-independently, suggesting that they are not cancerous. They differentiated into adipocytes, osteoblasts, and chondrocytes by treatment with certain stimuli. Moreover, following injection into the tail vein, the cells migrated into the wounded region of the liver and differentiated into hepatocytes. We succeeded in establishing several AD-MSC clonal cell lines that maintain the tissue-specific markers and characteristics of the developmental phase. These clonal cell lines will serve as important tools to study the mechanism of differentiation of MSCs. 相似文献
997.
998.
Eicosanoids are key mediators and regulators of inflammation and oxidative stress often used as biomarkers for diseases and pathological conditions such as cardiovascular and pulmonary diseases and cancer. Analytically, comprehensive and robust quantification of different eicosanoid species in a multi-method approach is problematic because most of these compounds are relatively unstable and may differ in their chemical properties. Here we describe a novel ultra-performance liquid chromatography-selected reaction monitoring mass spectroscopy (UPLC-SRM/MS) method for simultaneous quantification of key urinary eicosanoids, including the prostaglandins (PG) tetranor PGE-M, 8-iso-, and 2,3-dinor-8-iso-PGF2α; the thromboxanes (TXs) 11-dehydro- and 2,3-dinor-TXB2; leukotriene E4; and 12-hydroxyeicosatetraenoic acid. In contrast to previous methods, which used time-consuming and complex solid phase extraction, we prepared samples with a simple liquid/liquid extraction procedure. Because collision-induced dissociation produced characteristic product ions for all analytes, no derivatization step for SRM/MS analysis was necessary. Analytes were separated with a short UPLC reversed-phase column (1.7 µm particles), allowing shorter run times than conventional HPLC columns. The method was validated and applied to human urine samples showing excellent precision, accuracy, detection limits, and robustness. In summary, the developed method allows robust and sensitive profiling of urinary eicosanoid species, making it a useful and valuable tool for biomarker profiling in clinical/toxicological studies. 相似文献
999.
Alena S. Gsell Lisette N. de Senerpont Domis Anna Przytulska‐Bartosiewicz Wolf M. Mooij Ellen van Donk Bas W. Ibelings 《Journal of phycology》2012,48(5):1197-1208
Marine and freshwater phytoplankton populations often show large clonal diversity, which is in disagreement with clonal selection of the most vigorous genotype(s). Temporal fluctuation in selection pressures in variable environments is a leading explanation for maintenance of such genetic diversity. To test the influence of temperature as a selection force in continually (seasonally) changing aquatic systems we carried out reaction norms experiments on co‐occurring clonal genotypes of a ubiquitous diatom species, Asterionella formosa Hassall, across an environmentally relevant range of temperatures. We report within population genetic diversity and extensive diversity in genotype‐specific reaction norms in growth rates and cell size traits. Our results showed genotype by environment interactions, indicating that no genotype could outgrow all others across all temperature environments. Subsequently, we constructed a model to simulate the relative proportion of each genotype in a hypothetical population based on genotype and temperature‐specific population growth rates. This model was run with different seasonal temperature patterns. Our modeling exercise showed a succession of two to several genotypes becoming numerically dominant depending on the underlying temperature pattern. The results suggest that (temperature) context dependent fitness may contribute to the maintenance of genetic diversity in isolated populations of clonally reproducing microorganisms in temporally variable environments. 相似文献
1000.
Nishimura Y Shishido T Ishii J Tanaka T Ogino C Kondo A 《Journal of biotechnology》2012,157(1):124-129
Bio-nanocapsules (BNCs) are hollow nanoparticles composed of the L protein of hepatitis B virus (HBV) surface antigen (HBsAg), which can specifically introduce genes and drugs into various kinds of target cells. Although the classic electroporation method has typically been used to introduce highly charged molecules such as DNA, it is rarely adopted for proteins due to its very low efficiency. In this study, a novel approach to the preparation of BNC was established whereby a target protein was pre-encapsulated during the course of nanoparticle formation. Briefly, because of the process of BNC formation in a budding manner on the endoplasmic reticulum (ER) membrane, the association of target proteins to the ER membrane with lipidation sequences (ER membrane localization sequences) could directly generate protein-encapsulating BNC in collaboration with co-expression of the L proteins. Since the membrane-localized proteins are automatically enveloped into BNCs during the budding event, this method can be protect the proteins and BNCs from damage caused by electroporation and obviate the need for laborious consideration to study the optimal conditions for protein encapsulation. This approach would be a useful method for encapsulating therapeutic candidate proteins into BNCs. 相似文献