全文获取类型
收费全文 | 10353篇 |
免费 | 584篇 |
国内免费 | 32篇 |
专业分类
10969篇 |
出版年
2024年 | 27篇 |
2023年 | 115篇 |
2022年 | 357篇 |
2021年 | 543篇 |
2020年 | 332篇 |
2019年 | 425篇 |
2018年 | 455篇 |
2017年 | 328篇 |
2016年 | 472篇 |
2015年 | 534篇 |
2014年 | 638篇 |
2013年 | 805篇 |
2012年 | 846篇 |
2011年 | 726篇 |
2010年 | 441篇 |
2009年 | 356篇 |
2008年 | 444篇 |
2007年 | 445篇 |
2006年 | 389篇 |
2005年 | 387篇 |
2004年 | 298篇 |
2003年 | 252篇 |
2002年 | 227篇 |
2001年 | 111篇 |
2000年 | 98篇 |
1999年 | 80篇 |
1998年 | 60篇 |
1997年 | 31篇 |
1996年 | 36篇 |
1995年 | 41篇 |
1994年 | 26篇 |
1993年 | 28篇 |
1992年 | 47篇 |
1991年 | 42篇 |
1990年 | 46篇 |
1989年 | 42篇 |
1988年 | 44篇 |
1987年 | 33篇 |
1986年 | 30篇 |
1985年 | 37篇 |
1984年 | 33篇 |
1983年 | 27篇 |
1982年 | 21篇 |
1981年 | 26篇 |
1980年 | 13篇 |
1979年 | 16篇 |
1978年 | 20篇 |
1977年 | 14篇 |
1976年 | 22篇 |
1975年 | 17篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
Orme CD Davies RG Olson VA Thomas GH Ding TS Rasmussen PC Ridgely RS Stattersfield AJ Bennett PM Owens IP Blackburn TM Gaston KJ 《PLoS biology》2006,4(7):e208
Large-scale patterns of spatial variation in species geographic range size are central to many fundamental questions in macroecology and conservation biology. However, the global nature of these patterns has remained contentious, since previous studies have been geographically restricted and/or based on small taxonomic groups. Here, using a database on the breeding distributions of birds, we report the first (to our knowledge) global maps of variation in species range sizes for an entire taxonomic class. We show that range area does not follow a simple latitudinal pattern. Instead, the smallest range areas are attained on islands, in mountainous areas, and largely in the southern hemisphere. In contrast, bird species richness peaks around the equator, and towards higher latitudes. Despite these profoundly different latitudinal patterns, spatially explicit models reveal a weak tendency for areas with high species richness to house species with significantly smaller median range area. Taken together, these results show that for birds many spatial patterns in range size described in geographically restricted analyses do not reflect global rules. It remains to be discovered whether global patterns in geographic range size are best interpreted in terms of geographical variation in species assemblage packing, or in the rates of speciation, extinction, and dispersal that ultimately underlie biodiversity. 相似文献
52.
Shima Rajaei Saeed Karima Hessam Sepasi Tehrani Somayeh Shateri Somayeh Mahmoodi Baram Meisam Mahdavi Farzad Mokhtari Alimohammad Alimohammadi Abbas Tafakhori Abolfazl Amiri Vajiheh Aghamollaii Hamid Fatemi Masoumeh Rajabibazl Farzad Kobarfard Ali Gorji 《Journal of neurochemistry》2020,155(2):207-224
53.
Seven 9,10-seco-9,19-cyclolanostane arabinosides, named podocarpasides A-G (1-7), were isolated from the roots of Actaea podocarpa DC., a species closely related to black cohosh (a well known dietary supplement). Their structures were determined with the help of spectroscopic data including extensive 2D NMR spectroscopy. The isolates were found inactive, when tested for cytotoxic, estrogenic, and antioxidant activities in cell based assays. They were also tested for anticomplement activity against the classical pathway of complement system and only podocarpaside C (3) inhibited modest complement activity with an IC50 value of 200 microM. 相似文献
54.
Amir Ahmad Akhavan Ali Khamesipour Yavar Rassi Shaden Kamhawi Mohammad Hossein Arandian Niloufar Jalali-zand Niloufar Shareghi Mohammad Reza Yaghoobi-Ershadi 《Experimental parasitology》2010,126(4):552-556
Many rodent species act as reservoir hosts of zoonotic cutaneous leishmaniasis in endemic areas. In the present study a simple and reliable assay based on nested PCR was developed for the detection and identification of Leishmania parasites from rodent skin samples. We designed Leishmania-specific primers that successfully amplified ITS regions of Leishmania major, Leishmania gerbilli and Leishmania turanica using nested PCR. Out of 95 field collected Rhombomys opimus, 21 were positive by microscopic examination and 48 by nested PCR. The percentage of gerbils infected with L. major, L. gerbilli and L. turanica was 3.2%, 1.1% and 27.4%, respectively. In 15.8% of the rodents, we found mixed natural infections by L. major and L. turanica, 1.1% by L. major and L. gerbilli, and 2.1% by the three species. We concluded that this method is simple and reliable for detecting and identifying Leishmania species circulating in rodent populations. 相似文献
55.
Mohammadreza Nematollahi Mohsen Razeghi Sina Mehdizadeh Hamidreza Tabatabaee Soraya Piroozi Zahra Rojhani Shirazi Ali Rafiee 《PloS one》2016,11(2)
Anterior cruciate ligament injury is a debilitating pathology which may alter lower limb coordination pattern in both intact and affected lower extremities during activities of daily living. Emerging evidence supports the notion that kinematic variables may not be a good indicator to differentiate patients with anterior cruciate ligament deficiency during step descent task. The aim of the present study was to examine alterations in kinematics as well as coordination patterns and coordination variability of both limbs of these patients during a single step descent task. Continuous relative phase technique was used to measure coordination pattern and coordination variability between a group of anterior cruciate ligament deficient (n = 23) and a healthy control group (n = 23). A third order polynomial Curve fitting was utilized to provide a curve that best fitted to the data points of coordination pattern and coordination variability of the healthy control group. This was considered as a reference to compare to that of patient group using nonlinear regression analysis. The results of the present study demonstrated an altered coordination pattern of the supporting shank-thigh and the stepping foot-shank couplings in anterior cruciate ligament deficient subjects. It was further noticed that there was an increased coordination variability in foot-shank and shank-thigh couplings of both supporting and stepping legs. There was no significant difference in the hip, knee and ankle joints kinematics in either side of these patients. Anterior cruciate ligament deficient individuals showed altered strategies in both intact and affected legs, with increased coordination variability. Kinematic data did not indicate any significant difference between the two groups. It could be concluded that more sophisticated dynamic approach such as continuous relative phase would uncover discrepancies between the healthy and anterior cruciate ligament deficient individuals. 相似文献
56.
Faramarzi MA Tabatabaei Yazdi M Amini M Zarrini G Shafiee A 《FEMS microbiology letters》2003,222(2):183-186
Microbial hydroxylation of progesterone occurred in the culture of Acremonium strictum PTCC 5282 to produce two hydroxylated pregnene-like steroids. The metabolites were purified and characterized using spectroscopic methods and identified as 15alpha-hydroxyprogesterone and 15alpha-hydroxydeoxycorticosterone. 相似文献
57.
Bouchra Benmansour Feriel Youssef Manel Ben Ali Bander Albogami Fehmi Boufahja 《Saudi Journal of Biological Sciences》2022,29(5):3610-3616
Between 2018 and 2020, 696 fish belonging to two species of sharks from the Family Triakidae (Mustelus mustelus and M. punctulatus) were collected from the coasts of Tunisia and inspected for parasites. Six copepod taxa (Perissopus dentatus Steenstrup & Lütken, 1861, Eudactylinella alba Wilson, 1932, Kroyeria lineata Van Beneden, 1853, Nesippus orientalis Heller, 1865 and Lernaeopoda galei Krøyer, 1837, Kroyeria sp.), four isopod species (Anilocra physodes (Linnaeus, 1758), Emetha audouini (H. Milne Edwards, 1840), Ceratothoa parallela (Otto, 1828) and Ceratothoa oestroides (Risso, 1816)) and two monogenean species (Erpocotyle sp1. And Erpocotyle sp2) were collected. A large number of global host records was reported, including the occurrence of E. audouini on M. mustelus and of Erpocotyle sp.2 on M. punctulatus. The study of the diversity of parasites per host species revealed that M. mustelus had a higher parasitic richness compared to M. punctulatus. In this study, it was provided for the first records on ectoparasites on Triakidae sharks from Tunisian coasts and their infection indices. 相似文献
58.
McCulloch CC Kay DM Factor SA Samii A Nutt JG Higgins DS Griffith A Roberts JW Leis BC Montimurro JS Zabetian CP Payami H 《Human genetics》2008,123(3):257-265
The objective of this study was to explore combined effects of four candidate susceptibility genes and two exposures on Parkinson’s
disease (PD) risk; namely, α-synuclein (SNCA) promoter polymorphism REP1, microtubule-associated protein tau (MAPT) H1/H2 haplotypes, apolipoprotein E (APOE) ε2/ε3/ε4 polymorphism, ubiquitin carboxy-terminal esterase L1 (UCHL1) S18Y variant, cigarette smoking and caffeinated coffee consumption. 932 PD patients and 664 control subjects from the NeuroGenetics
Research Consortium, with complete data on all six factors, were studied. Uniform protocols were used for diagnosis, recruitment,
data collection and genotyping. A logistic regression model which included gene-exposure interactions was applied. Likelihood
ratio tests (LRTs) were used for significance testing and Bayesian inference was used to estimate odds ratios (ORs). MAPT (P = 0.007), SNCA REP1 (P = 0.012), smoking (P = 0.001), and coffee (P = 0.011) were associated with PD risk. Two novel interactions were detected: APOE with coffee (P = 0.005), and REP1 with smoking (P = 0.021). While the individual main effects were modest, each yielding OR < 1.6, the effects were cumulative, with some combinations
reaching OR = 12.6 (95% CI: 5.9–26.8). This study provides evidence for the long-held notion that PD risk is modulated by
cumulative and interactive effects of genes and exposures. Furthermore, the study demonstrates that while interaction studies
are useful for exploring risk relationships that might otherwise go undetected, results should be interpreted with caution
because of the inherent loss of power due to multiple testing. The novel findings of this study that warrant replication are
the evidence for interaction of coffee with APOE, and of smoking with REP1 on PD risk.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
59.
Ali Zohaib Muhammad Saqib Muhammad Ammar Athar Jing Chen Awais-ur-Rahman Sial Saeed Khan Zeeshan Taj Halima Sadia Usman Tahir Muhammad Haleem Tayyab Muhammad Asif Qureshi Muhammad Khalid Mansoor Muhammad Ahsan Naeem Bing-Jie Hu Bilal Ahmed Khan Ikram Din Ujjan Bei Li Wei Zhang Yun Luo Yan Zhu Cecilia Waruhiu Iahtasham Khan Xing-Lou Yang Muhammad Sohail Sajid Victor Max Corman Bing Yan Zheng-Li Shi 《中国病毒学》2018,33(5):410-417
Middle East Respiratory Syndrome Coronavirus (MERS-CoV) is a zoonotic pathogen capable of causing severe respiratory disease in humans. Although dromedary camels are considered as a major reservoir host, the MERS-CoV infection dynamics in camels are not fully understood. Through surveillance in Pakistan, nasal (n = 776) and serum (n = 1050)samples were collected from camels between November 2015 and February 2018. Samples were collected from animal markets, free-roaming herds and abattoirs. An in-house ELISA was developed to detect IgG against MERS-CoV. A total of 794 camels were found seropositive for MERS-CoV. Prevalence increased with the age and the highest seroprevalence was recorded in camels aged [ 10 years (81.37%) followed by those aged 3.1–10 years (78.65%) and B 3 years (58.19%).Higher prevalence was observed in female (78.13%) as compared to male (70.70%). Of the camel nasal swabs, 22 were found to be positive by RT-qPCR though with high Ct values. Moreover, 2,409 human serum samples were also collected from four provinces of Pakistan during 2016–2017. Among the sampled population, 840 humans were camel herders.Although we found a high rate of MERS-CoV antibody positive dromedaries (75.62%) in Pakistan, no neutralizing antibodies were detected in humans with and without contact to camels. 相似文献
60.
Ali Alsalme Nabil Al-Zaqri Rizwan Ullah Sidra Yaqub 《Saudi Journal of Biological Sciences》2021,28(3):1757-1762
Present study was designed to obtain estimation about ground water quality of Bhimber, Azad Jammu and Kashmir (AJK), Pakistan. A total of 12 water samples were collected from different localities of study area to analyze for various physicochemical and biological parameters i.e. namely temperature, pH, turbidity, color, odor, taste, electric conductivity (EC), total dissolved solids (TDS), total hardness (Calcium + Magnesium), chloride, arsenic, phosphate, lead, ammonium ion, nitrite, Fecal coliform and Escherichia coli. Results exposed that all ground water samples of study area were grossly contaminated with pathogenic microorganisms like E. coli and Fecal coliform except one water sample that was obtained from community filter plant Samahni Chowk site. Besides it, values of some physicochemical water quality determining parameters also deviated from recommended limits of World Health Organization (WHO). Chloride ion concentration was little below the prescribed limits in almost all water samples. It has been proven that consumption of un-safe drinking water is one of the major cause of prevalence of water borne diseases like diarrhea, gastroenteritis, typhoid fever and malaria etc. in study area. Community water supply and sanitation projects should be encouraged; government should provide filter plants in all regions of the country so that people could have easy approach to safe drinking water. 相似文献