全文获取类型
收费全文 | 1378篇 |
免费 | 81篇 |
出版年
2023年 | 6篇 |
2022年 | 22篇 |
2021年 | 43篇 |
2020年 | 12篇 |
2019年 | 29篇 |
2018年 | 61篇 |
2017年 | 37篇 |
2016年 | 49篇 |
2015年 | 67篇 |
2014年 | 94篇 |
2013年 | 102篇 |
2012年 | 100篇 |
2011年 | 109篇 |
2010年 | 61篇 |
2009年 | 43篇 |
2008年 | 88篇 |
2007年 | 76篇 |
2006年 | 72篇 |
2005年 | 71篇 |
2004年 | 56篇 |
2003年 | 44篇 |
2002年 | 50篇 |
2001年 | 11篇 |
2000年 | 11篇 |
1999年 | 8篇 |
1998年 | 9篇 |
1997年 | 6篇 |
1996年 | 8篇 |
1995年 | 10篇 |
1994年 | 3篇 |
1993年 | 5篇 |
1992年 | 6篇 |
1991年 | 5篇 |
1990年 | 6篇 |
1989年 | 5篇 |
1987年 | 6篇 |
1986年 | 4篇 |
1984年 | 4篇 |
1983年 | 3篇 |
1982年 | 4篇 |
1981年 | 5篇 |
1979年 | 3篇 |
1978年 | 5篇 |
1976年 | 3篇 |
1975年 | 3篇 |
1973年 | 6篇 |
1970年 | 5篇 |
1969年 | 2篇 |
1968年 | 6篇 |
1967年 | 2篇 |
排序方式: 共有1459条查询结果,搜索用时 15 毫秒
951.
952.
Ha?oń A Nowak-Markwitz E Donizy P Matkowski R Maciejczyk A Gansukh T Gy?rffy B Spaczyński M Zabel M Lage H Surowiak P 《The journal of histochemistry and cytochemistry》2012,60(7):491-501
Degradation of the extracellular matrix and basement membrane is a critical step in tumor progression. Matrix metalloproteinase 2 (MMP-2) and tissue inhibitor of metalloproteinase 2 (TIMP 2) act in a coordinated manner to form an integrated system involved in ovarian cancer (OC) progression. In this study, the authors describe the expression of TIMP-2 detected by immunohistochemistry in 6 OC cell lines and in 43 malignant epithelial ovarian tumors (in tumor and stromal compartments) in sections originating from primary laparotomies. No significant correlations between overall and progression-free survival and TIMP-2 expression in tumor compartment were observed. The analysis demonstrated a significant association between enhanced stromal expression of TIMP-2 and better clinical response to cisplatin- and paclitaxel-based chemotherapy. Increased expression of TIMP-2 in the stromal compartment and simultaneous overexpression in both stromal and tumor compartments strongly correlated with increased survival. No significant correlations were found in vitro between resistance to cisplatin, paclitaxel, or topotecan and the expression of TIMP-2 in the OC cell lines, suggesting stromal influences on tumor chemoresistance in the physiological environment. This study supports the concept of TIMP-2 expression in the stromal compartment of OC as a promising marker of prognosis and response to cisplatin- and paclitaxel-based chemotherapy in OC patients. 相似文献
953.
954.
C. Kevin Boyce Tim J. Brodribb Taylor S. Feild Maciej A. Zwieniecki 《Proceedings. Biological sciences / The Royal Society》2009,276(1663):1771-1776
The veins that irrigate leaves during photosynthesis are demonstrated to be strikingly more abundant in flowering plants than in any other vascular plant lineage. Angiosperm vein densities average 8 mm of vein per mm2 of leaf area and can reach 25 mm mm−2, whereas such high densities are absent from all other plants, living or extinct. Leaves of non-angiosperms have consistently averaged close to 2 mm mm−2 throughout 380 million years of evolution despite a complex history that has involved four or more independent origins of laminate leaves with many veins and dramatic changes in climate and atmospheric composition. We further demonstrate that the high leaf vein densities unique to the angiosperms enable unparalleled transpiration rates, extending previous work indicating a strong correlation between vein density and assimilation rates. Because vein density is directly measurable in fossils, these correlations provide new access to the physiology of extinct plants and how they may have impacted their environments. First, the high assimilation rates currently confined to the angiosperms among living plants are likely to have been unique throughout evolutionary history. Second, the transpiration-driven recycling of water that is important for bolstering precipitation in modern tropical rainforests might have been significantly less in a world before the angiosperms. 相似文献
955.
Rafał A. Bachorz Giovanni Lupica Maciej Gutowski Maciej Haranczyk 《Journal of molecular modeling》2009,15(7):817-827
Changes of electrostatic potential around the DNA molecule resulting from chemical modifications of nucleotides may play a
role in enzymatic recognition of damaged sites. The electrostatic potential around the DNA fragments containing either the
intact guanine-cytosine pair or 8-oxoguanine-cytosine or the guanine-abasic site was projected on a cylindrical surface around
the double helix. The 2D maps of EP of intact and damaged DNA fragments were compared using image analysis methods. Occurrence
of abasic site and 8-oxoguanine lesions were found to be reflected in the EP maps. In the case of the 8-oxoguanine lesion,
the two phosphate groups and countercations of the damaged strand are moved away from the lesion in opposite directions, whereas
they are moved in the same direction in the case of the abasic site lesion. The characteristic features of 8-oxoguanine lesion
might be identified in the major groove, whereas the features of abasic site lesion the minor groove.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
956.
Fedoruk-Wyszomirska A Giel-Pietraszuk M Wyszko E Szymański M Ciesiołka J Barciszewska MZ Barciszewski J 《Molecular biology reports》2009,36(7):1647-1650
The hepatitis delta virus (HDV) ribozyme is an RNA enzyme that catalyzes the site-specific trans-esterification reaction. Using high hydrostatic pressure (HHP) technique we showed that HDV ribozyme catalyzes the reaction
of RNA cleavage in the absence of magnesium ions according to mechanism of acidic hydrolysis of esters. HHP induces changes
of water structure, lowering pH and effect ribozyme catalytic site structure formation without magnesium. HHP, similarly to
magnesium ion at ambient pressure stabilizes the higher order RNA structure of HDV, but Mg2+ is not involved in the catalysis. Our results clearly support the new mechanism of HDV hydrolysis and show advantages of
using HHP in analysis of macromolecules interaction. 相似文献
957.
Panasiewicz M Domek H Hoser G Fedoryszak N Kawalec M Pacuszka T 《Cellular & molecular biology letters》2009,14(2):175-189
Gangliosides are characteristically enriched in various membrane domains that can be isolated as low density membrane fraction
insoluble in detergents (detergent-resistant membranes, DRMs) or obtained after homogenization and sonication in 0.5 M sodium
carbonate (low-density membranes, LDMs). We assessed the effect of the ceramide structure of four [3H]-labeled GM1 ganglioside molecular species (GM1s) taken up by HL-60 cells on their occurrence in LDMs, and compared it with
our previous observations for DRMs. All GM1s contained C18 sphingosine, which was acetylated in GM1(18:1/2) or acylated with
C14, C18 or C18:1 fatty acids (Fas) 相似文献
958.
Maciej Lazarczyk Patricia Cassonnet Christian Pons Yves Jacob Michel Favre 《Microbiology and molecular biology reviews》2009,73(2):348-370
Summary: Infections by human papillomaviruses (HPVs) are the most frequently occurring sexually transmitted diseases. The crucial role of genital oncogenic HPV in cervical carcinoma development is now well established. In contrast, the role of cutaneous HPV in skin cancer development remains a matter of debate. Cutaneous beta-HPV strains show an amazing ubiquity. The fact that a few oncogenic genotypes cause cancers in patients suffering from epidermodysplasia verruciformis is in sharp contrast to the unapparent course of infection in the general population. Our recent investigations revealed that a natural barrier exists in humans, which protects them against infection with these papillomaviruses. A central role in the function of this HPV-specific barrier is played by a complex of the zinc-transporting proteins EVER1, EVER2, and ZnT-1, which maintain cellular zinc homeostasis. Apparently, the deregulation of the cellular zinc balance emerges as an important step in the life cycles not only of cutaneous but also of genital HPVs, although the latter viruses have developed a mechanism by which they can break the barrier and impose a zinc imbalance. Herein, we present a previously unpublished list of the cellular partners of EVER proteins, which points to future directions concerning investigations of the mechanisms of action of the EVER/ZnT-1 complex. We also present a general overview of the pathogenesis of HPV infections, taking into account the latest discoveries regarding the role of cellular zinc homeostasis in the HPV life cycle. We propose a potential model for the mechanism of function of the anti-HPV barrier. 相似文献
959.
Hila Damari-Weissler Shimon Rachamilevitch Roni Aloni Marcelo A. German Shabtai Cohen Maciej A. Zwieniecki N. Michele Holbrook David Granot 《Planta》2009,230(4):795-805
It has been suggested that LeFRK2, the major fructose-phosphorylating enzyme in tomato plants, may be required for stem xylem development. Yet, we do not know
if this enzyme affects the development of individual vessels, whether it affects water conductance, or whether it affects
phloem development and sugar transport. Here, we show that suppression of LeFRK2 results in a significant reduction in the size of vascular cells and slows fiber maturation. The vessels in stems of LeFRK2-antisense plants are narrower than in WT plants and have thinner secondary cell walls. Although the cambium produces rounded
secondary vessels, these vessels become deformed during the early stages of xylem maturation. Water conductance is then reduced
in stems, roots, and leaves, suggesting that LeFRK2 influences xylem development throughout the entire vascular system. Interestingly, the build-up of positive xylem pressure
under static (no-flow) conditions was also decreased. Suppression of LeFRK2 reduced the length and width of the sieve elements, as well as callose deposition. To examine the effect of LeFRK2 suppression on phloem transport, we created triple-grafted plants in which a portion of the wild-type stem was replaced with
an antisense interstcok, and compared the contents of the transported sugar, sucrose, in the different portions of these stems.
Sucrose contents above and within the LeFRK2-antisense interstock were significantly higher than those below the graft. These results show that the antisense interstock
restricted the downward movement of sucrose, suggesting that LeFRK2 is required for both phloem and xylem development.
Contribution No. 114/2009 from the Volcani Center ARO. 相似文献
960.
Maciej Pietr Rivka Levy Yi Hsing Lin Nephi Stella Zvi Vogel Ana Juknat 《FEBS letters》2009,583(12):2071-122
We examined how lipopolysaccharide (LPS) and interferon gamma (IFN-γ), known to differentially activate microglia, affect the expression of G protein-coupled receptor 55 (GPR55), a novel cannabinoid receptor. We found that GPR55 mRNA is significantly expressed in both primary mouse microglia and the BV-2 mouse microglial cell line, and that LPS down-regulates this message. Conversely, IFN-γ slightly decreases GPR55 mRNA in primary microglia, while it upregulates this message in BV-2 cells. Moreover, the GPR55 agonist, lysophosphatidylinositol, increases ERK phosphorylation in BV-2 stimulated with IFN-γ, in correlation with the increased amount of GPR55 mRNA. Remarkably, these stimuli-induced changes in GPR55 expression are similar to those observed with CB2-R, suggesting that both receptors might be involved in neuroinflammation and that their expression is concomitantly controlled by the state of microglial activation. 相似文献