全文获取类型
收费全文 | 13188篇 |
免费 | 947篇 |
国内免费 | 4篇 |
出版年
2021年 | 107篇 |
2020年 | 106篇 |
2019年 | 147篇 |
2018年 | 176篇 |
2017年 | 176篇 |
2016年 | 245篇 |
2015年 | 421篇 |
2014年 | 406篇 |
2013年 | 608篇 |
2012年 | 740篇 |
2011年 | 653篇 |
2010年 | 510篇 |
2009年 | 409篇 |
2008年 | 600篇 |
2007年 | 598篇 |
2006年 | 595篇 |
2005年 | 591篇 |
2004年 | 582篇 |
2003年 | 587篇 |
2002年 | 561篇 |
2001年 | 151篇 |
2000年 | 107篇 |
1999年 | 140篇 |
1998年 | 177篇 |
1997年 | 159篇 |
1996年 | 150篇 |
1995年 | 171篇 |
1994年 | 136篇 |
1993年 | 170篇 |
1992年 | 126篇 |
1991年 | 147篇 |
1990年 | 141篇 |
1989年 | 111篇 |
1988年 | 130篇 |
1987年 | 122篇 |
1986年 | 96篇 |
1985年 | 121篇 |
1984年 | 181篇 |
1983年 | 153篇 |
1982年 | 147篇 |
1981年 | 156篇 |
1980年 | 124篇 |
1979年 | 117篇 |
1978年 | 137篇 |
1977年 | 104篇 |
1976年 | 90篇 |
1975年 | 100篇 |
1974年 | 85篇 |
1973年 | 75篇 |
1970年 | 66篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
2.
Johanna Ceschin Hans Caspar Hürlimann Christelle Saint-Marc Delphine Albrecht Typhaine Violo Michel Moenner Bertrand Daignan-Fornier Beno?t Pinson 《The Journal of biological chemistry》2015,290(39):23947-23959
5-Aminoimidazole-4-carboxamide-1-β-d-ribofuranoside monophosphate (AICAR) is a natural metabolite with potent anti-proliferative and low energy mimetic properties. At high concentration, AICAR is toxic for yeast and mammalian cells, but the molecular basis of this toxicity is poorly understood. Here, we report the identification of yeast purine salvage pathway mutants that are synthetically lethal with AICAR accumulation. Genetic suppression revealed that this synthetic lethality is in part due to low expression of adenine phosphoribosyl transferase under high AICAR conditions. In addition, metabolite profiling points to the AICAR/NTP balance as crucial for optimal utilization of glucose as a carbon source. Indeed, we found that AICAR toxicity in yeast and human cells is alleviated when glucose is replaced by an alternative carbon source. Together, our metabolic analyses unveil the AICAR/NTP balance as a major factor of AICAR antiproliferative effects. 相似文献
3.
4.
Primary skeletal muscle cells cultured on gelatin bead microcarriers develop structural and biochemical features characteristic of adult skeletal muscle 下载免费PDF全文
5.
Packed Bed Bioreactor for the Isolation and Expansion of Placental-Derived Mesenchymal Stromal Cells
Michael J. Osiecki Thomas D. Michl Betul Kul Babur Mahboubeh Kabiri Kerry Atkinson William B. Lott Hans J. Griesser Michael R. Doran 《PloS one》2015,10(12)
Large numbers of Mesenchymal stem/stromal cells (MSCs) are required for clinical relevant doses to treat a number of diseases. To economically manufacture these MSCs, an automated bioreactor system will be required. Herein we describe the development of a scalable closed-system, packed bed bioreactor suitable for large-scale MSCs expansion. The packed bed was formed from fused polystyrene pellets that were air plasma treated to endow them with a surface chemistry similar to traditional tissue culture plastic. The packed bed was encased within a gas permeable shell to decouple the medium nutrient supply and gas exchange. This enabled a significant reduction in medium flow rates, thus reducing shear and even facilitating single pass medium exchange. The system was optimised in a small-scale bioreactor format (160 cm2) with murine-derived green fluorescent protein-expressing MSCs, and then scaled-up to a 2800 cm2 format. We demonstrated that placental derived MSCs could be isolated directly within the bioreactor and subsequently expanded. Our results demonstrate that the closed system large-scale packed bed bioreactor is an effective and scalable tool for large-scale isolation and expansion of MSCs. 相似文献
6.
Preben D. Thomsen Hanne Qvist Lena Marklund Leif Andersson Hans Sjöström Ove Norén 《Mammalian genome》1993,4(10):604-607
A porcine 2-kb partial dipeptidylpeptidase IV (DPP4, EC 3.4.14.5) cDNA clone and a porcine 16-kb genomic fragment containing parts of the DPP4 gene were isolated, characterized, and used as probes to map the DPP4 gene to pig Chr (Chr) 15q21 by fluorescence in situ hybridization. A two-allele RFLP was revealed for the DPP4 gene. This polymorphism was utilized in a linkage test against the erythrocyte antigen G (EAG), previously assigned to Chr 15, and the microsatellite S0088, which is linked to EAG. The linkage analyses revealed significant evidence for linkage confirming the assignment of DPP4 to Chr 15. 相似文献
7.
Subcellular volumes and metabolite concentrations in barley leaves 总被引:26,自引:1,他引:25
Metabolite concentrations in subcellular compartments from mature barley (Hordeum vulgare L. cv. Apex) leaves after 9 h of illumination and 5 h of darkness were determined by nonaqueous fractionation and by the stereological evaluation of cellular and subcellular volumes from light and electron micrographs. Twenty one-day-old primary leaves of barley with a total leaf volume of 902 μL per mg chlorophyll were found to be composed of 27% epidermis, 42% mesophyll cells, 6% veins, 4.5% apoplast and 23% gas space. While in epidermal cells 99% of the volume was occupied by the vacuole, mesophyll cells with an average volume of 31.3 pL consisted of 23 pL (73%) vacuole, 4.6 pL (19%) chloroplasts, 2.06 pL (6,7%) cytosol (including smaller organelles and vesicles), 0.34 pL (1%) mitochondria and 107 fL (0.34%) nucleus. The differences between leaves harvested after 9 h of illumination and after 5 h of darkness were in the size of the stromal compartment and the starch grains therein. Subcellular metabolite concentrations were calculated from the compartmental volumes and metabolite contents of the compartments as determined by nonaqueous fractionation. The amino-acid concentrations in stroma and cytosol were rather similar after 9 h of illumination and 5 h of darkness. In contrast, the vacuolar amino-acid concentrations were about one order of magnitude lower than the stroma and cytosol values, and there was a slight increase in concentration after 5 h of darkness. 相似文献
8.
Cees Hol Cees M. Verduin Etienne E.A. Van Dijke Jan Verhoef ré Fleer Hans van Dijk 《FEMS immunology and medical microbiology》1995,11(3):207-211
Abstract The purpose of this study was to investigate complement resistance in Branhamella (Moraxella) catarrhalis isolated from healthy schoolchildren or sputum-producing adult patients. Two techniques were used: a serum bactericidal assay as the gold standard and an easier ‘culture and spot’ test. Children (age 4–13; n = 303) and patients ( n = 1047) showed high colonization/infection rates with B. catarrhalis (31% and 19%, respectively). Complement resistance or intermediate sensitivity occurred frequently in patient isolates (62% and 27%, respectively) and less often in children (33% and 8.5%, respectively; P ⪡ 0.0001). In young children (age 4–5 years), the proportion of complement-resistant strains was around 50%. Complement resistance in B. catarrhalis is associated with illness and may hence be considered a virulence factor. 相似文献
9.
10.
Richard P. Shefferson Tiiu Kull Michael J. Hutchings Marc‐André Selosse Hans Jacquemyn Kimberly M. Kellett Eric S. Menges Richard B. Primack Juha Tuomi Kirsi Alahuhta Sonja Hurskainen Helen M. Alexander Derek S. Anderson Rein Brys Emilia Brzosko Slavomir Dostálik Katharine Gregg Zdeněk Ipser Anne Jäkäläniemi Jana Jersáková W. Dean Kettle Melissa K. McCormick Ana Mendoza Michael T. Miller Asbjørn Moen Dag‐Inge Øien Ülle Püttsepp Mélanie Roy Nancy Sather Nina Sletvold Zuzana Štípková Kadri Tali Robert J. Warren II Dennis F. Whigham 《Ecology letters》2018,21(5):724-733
Vegetative dormancy, that is the temporary absence of aboveground growth for ≥ 1 year, is paradoxical, because plants cannot photosynthesise or flower during dormant periods. We test ecological and evolutionary hypotheses for its widespread persistence. We show that dormancy has evolved numerous times. Most species displaying dormancy exhibit life‐history costs of sprouting, and of dormancy. Short‐lived and mycoheterotrophic species have higher proportions of dormant plants than long‐lived species and species with other nutritional modes. Foliage loss is associated with higher future dormancy levels, suggesting that carbon limitation promotes dormancy. Maximum dormancy duration is shorter under higher precipitation and at higher latitudes, the latter suggesting an important role for competition or herbivory. Study length affects estimates of some demographic parameters. Our results identify life historical and environmental drivers of dormancy. We also highlight the evolutionary importance of the little understood costs of sprouting and growth, latitudinal stress gradients and mixed nutritional modes. 相似文献