全文获取类型
收费全文 | 3720篇 |
免费 | 283篇 |
专业分类
4003篇 |
出版年
2022年 | 34篇 |
2021年 | 38篇 |
2020年 | 35篇 |
2019年 | 27篇 |
2018年 | 58篇 |
2017年 | 37篇 |
2016年 | 81篇 |
2015年 | 124篇 |
2014年 | 117篇 |
2013年 | 205篇 |
2012年 | 252篇 |
2011年 | 236篇 |
2010年 | 164篇 |
2009年 | 175篇 |
2008年 | 203篇 |
2007年 | 182篇 |
2006年 | 172篇 |
2005年 | 196篇 |
2004年 | 183篇 |
2003年 | 169篇 |
2002年 | 159篇 |
2001年 | 30篇 |
2000年 | 41篇 |
1999年 | 46篇 |
1998年 | 63篇 |
1997年 | 39篇 |
1996年 | 38篇 |
1995年 | 44篇 |
1994年 | 39篇 |
1993年 | 41篇 |
1992年 | 41篇 |
1991年 | 29篇 |
1990年 | 15篇 |
1989年 | 21篇 |
1988年 | 19篇 |
1987年 | 20篇 |
1985年 | 27篇 |
1984年 | 25篇 |
1983年 | 20篇 |
1982年 | 27篇 |
1981年 | 28篇 |
1980年 | 29篇 |
1979年 | 29篇 |
1978年 | 34篇 |
1977年 | 21篇 |
1976年 | 19篇 |
1974年 | 15篇 |
1973年 | 18篇 |
1970年 | 14篇 |
1957年 | 16篇 |
排序方式: 共有4003条查询结果,搜索用时 0 毫秒
31.
32.
Underiner TL Ruggeri B Aimone L Albom M Angeles T Chang H Hudkins RL Hunter K Josef K Robinson C Weinberg L Yang S Zulli A 《Bioorganic & medicinal chemistry letters》2008,18(7):2368-2372
Orally bioavailable, dual inhibitors of TIE-2/VEGF-R2 were identified by elaborating the C3/N13 SAR around a fused pyrrolodihydroindazolocarbazole scaffold. Analogs bearing a C3-thiophencarbonyl group were evaluated in enzymatic and cellular biochemical assays; two orally bioavailable analogs were further profiled in functional assays and found to inhibit microvessel growth in rat aortic explant cultures and inhibit Ang-1-stimulated chemotaxis of HUVECs. 相似文献
33.
In this paper, the effect of clinical symptoms of uterine inflammation on progesterone profile characteristics was quantified in dairy cows. A continuous scale based on visual observation of vaginal discharge (the previously developed D-index) was used to describe the clinical symptoms. Progesterone profiles in milk were used to describe the ovarian cycles, and to determine the distinguishing features of these profiles, a multivariate statistical procedure (principal component analysis) was performed.Significant negative effects of the D-index were seen during the first and second postpartum ovarian cycles. The D-index had a significant effect on the shape of progesterone profiles and the length of the ovarian cycles but it only accounted for a small proportion of the variation in these ovarian cycle features. The D-index was not a significant risk factor for the length of postpartum anovulatory period in the present study. 相似文献
34.
For either clinical or research purposes, the timing of the nocturnal onset in production of the urinary melatonin metabolite 6-sulfatoxymelatonin (UaMT6s-onset), has been proposed as a reliable and robust marker of circa-dian phase. However, given that most circadian rhythms show cycle-to-cycle variability, the statistical reliability of phase estimates obtained from a single study using UaMT6s-onset remains to be determined. Following 2 weeks of sleep diary and wrist actigraphy, 15 young, healthy good sleepers participated in four UaMT6s sampling sessions spaced 1 day apart. During the sampling sessions subjects remained indoors under low light conditions and hourly urine samples were collected from 19:00 to 02:00 h. Samples were subsequently assayed for UaMT6s using standard radioimmunographic techniques. UaMT6s-onset was determined by the time at which melatonin production exceeded the average of three proceeding trials by 100%. Sleep onset times were derived from sleep diary and actigraphic measures taken before the melatonin collection nights. We found that there was no significant variation between nights in group mean UaMT6s-onset times, and intraindividual variability was small. In addition, UaMT6s-onset times were highly and significantly correlated between nights (grand mean r = 0.804). Our results suggest that within 95% confidence interval limits, individual UaMT6s-onset estimates obtained from a single night UaMT6s-onset study can be used to predict subsequent UaMT6s-onset times within ±97 min. A close temporal relationship was also found between the timing of UaMT6s-onset and sleep onset. Overall, our results suggest that under entrained conditions single-session UaMT6s-onset studies can provide reliable individual UaMT6s-onset phase estimates and that the protocol described in this study is a practical and noninvasive methodology. (Chronobiology International, 13(6), 411-421, 1996) 相似文献
35.
Gastroprotective,cytoprotective and antioxidant effects of Oleum cinnamomi on ethanol induced damage
Cansu Ozbayer Hulyam Kurt Zeynep Ozdemir Tunc Tuncel Selva Moheb Saadat Dilek Burukoglu Hakan Senturk Irfan Degirmenci Hasan Veysi Gunes 《Cytotechnology》2014,66(3):431-441
Peptic ulcer disease is a gastrointestinal disorder defined by mucosal damage and free oxygen radicals associated with peptic ulcer and gastritis. Cinnamon is a traditional herb used for many diseases and it has also effects as an antioxidant, anti-inflammatory, antispasmodic and anti-ulcerative. Our research is based on oxidative stress and effects of Oleum cinnamomi on stomach, liver and kidney disorders induced by ethanol. In our experiment, 2–3 month old male Sprague–Dawley rats were used. One hour before the mucosal damage induced by 70 % ethanol, O. cinnamomi (2.5 ml/kg) was added into the groups. Gastric pH, analysis of gastric mucus and ulcer index were calculated from samples obtained from the stomach. Superoxide dismutase (SOD), malondialdehyde and catalase (CAT) levels were determined in stomach, liver and kidney homogenates and erythrocyte hemolysate. Histopathological examination of stomach, liver and kidney were determined with H&E staining. The non-treated ulcerative group showed higher scores than the control group which was treated with O. cinnamomi, when ulcer scores, gastric mucus and pH level of stomach are compared. Increased lipid peroxidation levels were observed in the liver, kidney and erythrocyte hemolysate. SOD activity was decreased in liver whereas increased in stomach of ethanol treated ulcerative groups. CAT levels were increased in stomach and liver of ethanol treated rats. Histopathological findings showed that ethanol treatment cause multiply organ damage such as stomach, liver and kidney injury. O. cinnamomi treatment protected these tissues from ethanol-induced damage. Consequently, the current investigation shows that O. cinnamomi has protective effects on ethanol-induced oxidative and mucosal damage. 相似文献
36.
Julie Hoover-Fong Nara Sobreira Julie Jurgens Peggy Modaff Carrie Blout Ann Moser Ok-Hwa Kim Tae-Joon Cho Sung?Yoon Cho Sang?Jin Kim Dong-Kyu Jin Hiroshi Kitoh Woong-Yang Park Hua Ling Kurt?N. Hetrick Kimberly?F. Doheny David Valle Richard?M. Pauli 《American journal of human genetics》2014,94(1):105-112
37.
38.
Margaret A. Johnson Maurice W. Southworth Francine B. Perler Kurt Wüthrich 《Biomolecular NMR assignments》2007,1(1):19-21
The backbone and side chain resonance assignments of a precursor of the KlbA intein from Methanococcus jannaschii have been determined, based on triple-resonance experiments with the uniformly [13C,15N]-labeled protein. 相似文献
39.
Coinfection with human immunodeficiency virus type-1 (HIV-1) and hepatitis C virus (HCV) is a global problem that is more prevalent in injection drug users because they have a higher risk for acquiring both viruses. The roles of inflammatory cytokines and oxidative stress were examined in HIV-1- and HCV-coinfected human hepatic cells. Morphine (the bioactive product of heroin), HIV-1 Tat and the MN strain gp120 (gp120(MN)) proteins, and X4 HIV-1(LAI/IIIB) and R5 HIV-1(SF162) isolates were used to study the mechanisms of disease progression in HCV (JFH1)-infected Huh7.5.1 cell populations. HCV increased tumor necrosis factor-α (TNF-α) and interleukin-6 (IL-6) release and augmented production of reactive oxygen species (ROS), nitric oxide (NO), and 3-nitrotyrosine (3-NT) in Huh7.5.1 cells. Morphine preferentially affected R5-tropic, but not X4-tropic, HIV-1 interactions with Huh7.5.1 cells. HIV-1 proteins or isolates increased cytokine release in HCV-infected cells, while adding morphine to coinfected cells caused complex imbalances, significantly disrupting cytokine secretion depending on the cytokine, morphine concentration, exposure duration, and particular pathogen involved. Production of ROS, NO, and 3-NT increased significantly in HCV- and HIV-1-coexposed cells while exposure to morphine further increased ROS. The proteasome inhibitor MG132 significantly decreased oxyradicals, cytokine levels, and HCV protein levels. Our findings indicate that hepatic inflammation is increased by combined exposure to HCV and HIV-1, that the ubiquitin-proteasome system and NF-κB contribute to key aspects of the response, and that morphine further exacerbates the disruption of host defenses. The results suggest that opioid abuse and HIV-1 coinfection each further accelerate HCV-mediated liver disease by dysregulating immune defenses. 相似文献
40.
Landscape correlates of forest plant invasions: A high‐resolution analysis across the eastern United States 下载免费PDF全文
Kurt Riitters Kevin Potter Basil V. Iannone III Christopher Oswalt Songlin Fei Qinfeng Guo 《Diversity & distributions》2018,24(3):274-284