全文获取类型
收费全文 | 3192篇 |
免费 | 207篇 |
专业分类
3399篇 |
出版年
2023年 | 14篇 |
2022年 | 30篇 |
2021年 | 51篇 |
2020年 | 39篇 |
2019年 | 58篇 |
2018年 | 79篇 |
2017年 | 55篇 |
2016年 | 83篇 |
2015年 | 131篇 |
2014年 | 142篇 |
2013年 | 227篇 |
2012年 | 242篇 |
2011年 | 251篇 |
2010年 | 153篇 |
2009年 | 122篇 |
2008年 | 215篇 |
2007年 | 218篇 |
2006年 | 179篇 |
2005年 | 150篇 |
2004年 | 149篇 |
2003年 | 158篇 |
2002年 | 158篇 |
2001年 | 27篇 |
2000年 | 15篇 |
1999年 | 25篇 |
1998年 | 26篇 |
1997年 | 32篇 |
1996年 | 20篇 |
1995年 | 29篇 |
1994年 | 22篇 |
1993年 | 22篇 |
1992年 | 25篇 |
1991年 | 23篇 |
1990年 | 26篇 |
1989年 | 11篇 |
1988年 | 11篇 |
1987年 | 13篇 |
1986年 | 10篇 |
1985年 | 13篇 |
1984年 | 15篇 |
1983年 | 8篇 |
1982年 | 11篇 |
1981年 | 17篇 |
1980年 | 12篇 |
1979年 | 8篇 |
1978年 | 8篇 |
1977年 | 8篇 |
1976年 | 10篇 |
1975年 | 7篇 |
1971年 | 4篇 |
排序方式: 共有3399条查询结果,搜索用时 15 毫秒
51.
Mirko Di Febbraro Peter W. W. Lurz Piero Genovesi Luigi Maiorano Marco Girardello Sandro Bertolino 《PloS one》2013,8(7)
Species introduction represents one of the most serious threats for biodiversity. The realized climatic niche of an invasive species can be used to predict its potential distribution in new areas, providing a basis for screening procedures in the compilation of black and white lists to prevent new introductions. We tested this assertion by modeling the realized climatic niche of the Eastern grey squirrel Sciurus carolinensis. Maxent was used to develop three models: one considering only records from the native range (NRM), a second including records from native and invasive range (NIRM), a third calibrated with invasive occurrences and projected in the native range (RCM). Niche conservatism was tested considering both a niche equivalency and a niche similarity test. NRM failed to predict suitable parts of the currently invaded range in Europe, while RCM underestimated the suitability in the native range. NIRM accurately predicted both the native and invasive range. The niche equivalency hypothesis was rejected due to a significant difference between the grey squirrel’s niche in native and invasive ranges. The niche similarity test yielded no significant results. Our analyses support the hypothesis of a shift in the species’ climatic niche in the area of introductions. Species Distribution Models (SDMs) appear to be a useful tool in the compilation of black lists, allowing identifying areas vulnerable to invasions. We advise caution in the use of SDMs based only on the native range of a species for the compilation of white lists for other geographic areas, due to the significant risk of underestimating its potential invasive range. 相似文献
52.
53.
José Eduardo Marqués-Gálvez Alfonso Navarro-Ródenas José Javier Peguero-Pina Francisco Arenas Angel Luigi Guarnizo Eustaquio Gil-Pelegrín Asunción Morte 《Physiologia plantarum》2020,170(4):537-549
Predicted increases in atmospheric concentration of carbon dioxide (CO2) coupled with increased temperatures and drought are expected to strongly influence the development of most of the plant species in the world, especially in areas with high risk of desertification like the Mediterranean basin. Helianthemum almeriense is an ecologically important Mediterranean shrub with an added interest because it serves as the host for the Terfezia claveryi mycorrhizal fungus, which is a desert truffle with increasingly commercial interest. Although both plant and fungi are known to be well adapted to dry conditions, it is still uncertain how the increase in atmospheric CO2 will influence them. In this article we have addressed the physiological responses of H. almeriense × T. claveryi mycorrhizal plants to increases in atmospheric CO2 coupled with drought and high vapor pressure deficit. This work reports one of the few estimations of mesophyll conductance in a drought deciduous Mediterranean shrub and evaluates its role in photosynthesis limitation. High atmospheric CO2 concentrations help desert truffle mycorrhizal plants to cope with the adverse effects of progressive drought during Mediterranean springs by improving carbon net assimilation, intrinsic water use efficiency and dispersal of the species through increased flowering events. 相似文献
54.
Gunnar Ottleben Luigi Messori Heinz Rüterjans Robert Kaptein Michèle Granger-Schnarr Manfred Schnarr 《Journal of biomolecular structure & dynamics》2013,31(3):447-461
Abstract A synthetic half-operator DNA-duplex, d(GCTACTGTATGT), containing a portion of the proposed recognition sequence (CTGT) of serveral “SOS” genes, has been synthesized. The dodecamer has been characterized through 1H-NMR spectroscopy. Complete assignment of exchangeable hydrogen bonded imino protons has been acheived by applying 1D NOE techniques and an analysis of the temperature dependence of the chemical shifts. In order to determine the specific role of the CTGT consensus sequence in the overall recognition process, the oligonucleotide duplex has been titrated with the amino terminal DNA binding domain of the LexA repressor. The observation of substantial changes of 1H-NMR chemical shifts in the imino proton region upon interaction with the protein strongly suggests that the protein binds specifically to the operator DNA. The largest deviations of 1H-NMR chemical shifts upon protein binding have been observed for protons assigned to the CTGT segment, thus strongly suggesting a direct involvement of this sequence in the binding process. At high potassium chloride concentrations the 1H-NMR chemical shift deviations are reverted which is consistent with the known drop in the affinity constant of LexA for operator DNA at high salt concentrations. 相似文献
55.
56.
Vittorio D'Urso Valentina Doneddu Irene Marchesi Angelo Collodoro Pietro Pirina Antonio Giordano Luigi Bagella 《Journal of cellular physiology》2013,228(5):945-951
Lung cancer is the leading cause of cancer‐related deaths over the world, characterized by a very high mortality rate. Molecular technique development tries to focus on early detection of cancers by studying molecular alterations that characterize cancer cells. Worldwide lung cancer research has focused on an ever‐increasing number of molecular elements of carcinogenesis at genetic, epigenetic and protein levels. The non‐invasiveness is the characteristic that all clinical trials on cancer detection should have. Abnormal chest imaging and/or non‐specific symptoms are initial signals of lung cancer that appear in an advanced stage of disease. This fact represents the cause of the low 5‐year survival rate: over 90% of patients dying within 5 years of diagnosis. Since smokers have higher quantity of sputum containing exfoliated cells from the bronchial tree, and the sputum represents the most easily accessible biological fluid and its collection is non‐invasive, analysis of this sample represents a good area of research in early lung cancer diagnosis. Continued cigarette smoking is the cause of chronic obstructive pulmonary disease (COPD), with an estimated attributable risk factor exceeding 80% in smoking affected individuals. Lung cancer is found in 40–70% of patients with COPD, particularly in severe disease, and it is a common cause of death in these patients. A large prospective trial of almost half a million non‐smokers showed as lung cancer is also common in patients with COPD who have never smoked. This review describes issues related to early lung cancer screening using non‐invasive methods. J. Cell. Physiol. © 2012 Wiley Periodicals, Inc. 相似文献
57.
58.
59.
Natural l-homocysteine and l,l-cystathionine, along with a series of unnatural analogues, have been prepared from l-aspartic and l-glutamic acid. Manipulation of the protected derivatives provided ω-iodoamino acids, which were used in thioalkylation reactions of sulfur nucleophiles, such as the ester of l-cysteine and potassium thioacetate. 相似文献
60.
Luciano Pirone Luigi Vitagliano Sonia Di Gaetano Emilia Pedone 《Journal of molecular recognition : JMR》2013,26(10):488-495
Recent investigations have shown that members of the KCTD family play important roles in fundamental biological processes. Despite their roles, very limited information is available on their structures and molecular organization. By combining different experimental and theoretical techniques, we have here characterized the two folded domains of KCTD12, an integral component and modulator of the GABAB2 receptor. Secondary prediction methods and CD spectroscopy have shown that the N‐terminal domain KCTD12BTB assumes an α/β structure, whereas the C‐terminal domain KCTD12H1 is predominantly characterized by a β‐structure. Binding assays indicate that the two domains independently expressed show a good affinity for each other. This suggests that the overall protein is likely endowed with a rather compact structure with two interacting structured domains joint by a long disordered region. Notably, both KCTD12BTB and KCTD12H1 are tetrameric when individually expressed. This finding could modify the traditional view that ascribes only to POZ/BTB domain a specific oligomerization role. The first quantification of the affinity of KCTD12POZ/BTB for the C‐terminal region of GABAB2 shows that it falls in the low micromolar range. Interestingly, we also demonstrate that a GABAB2‐related peptide is able to bind KCTD12BTB with a very high affinity. This peptide may represent a useful tool for modulating KCTD12/GABAB2 interaction in vitro and may also constitute the starting point for the development of peptidomimetic compounds with a potential for therapeutic applications. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献