全文获取类型
收费全文 | 12999篇 |
免费 | 1189篇 |
国内免费 | 1篇 |
出版年
2021年 | 169篇 |
2020年 | 126篇 |
2019年 | 150篇 |
2018年 | 158篇 |
2017年 | 163篇 |
2016年 | 275篇 |
2015年 | 510篇 |
2014年 | 522篇 |
2013年 | 651篇 |
2012年 | 885篇 |
2011年 | 778篇 |
2010年 | 534篇 |
2009年 | 437篇 |
2008年 | 670篇 |
2007年 | 659篇 |
2006年 | 590篇 |
2005年 | 554篇 |
2004年 | 538篇 |
2003年 | 548篇 |
2002年 | 465篇 |
2001年 | 293篇 |
2000年 | 245篇 |
1999年 | 254篇 |
1998年 | 134篇 |
1997年 | 115篇 |
1996年 | 127篇 |
1995年 | 119篇 |
1994年 | 96篇 |
1993年 | 110篇 |
1992年 | 188篇 |
1991年 | 176篇 |
1990年 | 133篇 |
1989年 | 142篇 |
1988年 | 143篇 |
1987年 | 120篇 |
1986年 | 107篇 |
1985年 | 118篇 |
1984年 | 115篇 |
1983年 | 91篇 |
1982年 | 73篇 |
1981年 | 68篇 |
1979年 | 90篇 |
1978年 | 81篇 |
1977年 | 78篇 |
1976年 | 59篇 |
1975年 | 49篇 |
1974年 | 90篇 |
1973年 | 59篇 |
1972年 | 66篇 |
1970年 | 63篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
2.
Ivania Pereira Stephanie Weber Stephan Holzer Georg Fischer Clemens Vass Hemma Resch 《PloS one》2015,10(3)
This work intends to assess circumpapillary retinal vessel density (RVD) at a 3.46 mm diameter circle and correlate it with circumpapillary retinal nerve fiber layer (RNFL) thickness measured with Fourier-Domain Optical Coherence Tomography. Furthermore, it aims to evaluate the reduction of intersubject variability of RNFL when considering RVD as a source of information for RNFL distribution. For that, 106 healthy subjects underwent circumpapillary RNFL measurement. Using the scanning laser ophthalmoscope fundus image, thickness and position of retinal vessels were assessed and integrated in a 256-sector RVD profile. The relationship between local RVD value and local RNFL thickness was modeled by linear regression. RNFL was then compensated for RVD variation by regression formulas. A strong statistically significant intrasubject correlation was found for all subjects between RVD and RNFL profiles (mean R = 0.769). In the intersubject regression analysis, 247 of 256 RNFL sectors showed a statistically significant positive correlation with RVD (mean R = 0.423). RVD compensation of RNFL resulted in a relative reduction of up to 20% of the intersubject variance. In conclusion, RVD in a 3.46mm circle has a clinically relevant influence on the RNFL distribution. RVD may be used to develop more individualized normative values for RNFL measurement, which might improve early diagnosis of glaucoma. 相似文献
3.
The nocturnally active weakly electric fish Gnathonemus petersii is known to employ active electrolocation for the detection of objects and for orientation in its environment. The fish emits pulse‐type electric signals with an electric organ and perceives these signals with more than 3,000 epidermal electroreceptor organs, the mormyromasts, which are distributed over the animal's skin surface. In this study, we measured the metric dimensions of the mormyromasts from different body regions to find structural and functional specialization of the various body parts. We focused on the two foveal regions of G. petersii, which are located at the elongated and movable chin (the Schnauzenorgan; SO) and at the nasal region (NR), the skin region between the mouth and the nares. These two foveal regions were compared to the dorsal part (back) of the fish, which contains typical nonfoveal mormyromasts. While the gross anatomy of the mormyromasts from all skin regions is similar, the metric dimensions of the main substructures differed. The mormyromasts at the SO are the smallest and contain the smallest receptor cells. In addition, the number of receptor cells per organ is lowest at the SO. In contrast, at the back the biggest receptor organs with the highest amount of receptor cells per organ occur. The mormyromasts at the NR are in several respects intermediate between those from the back and the SO. However, mormyromasts at the NR are longer than those at all other skin regions, the canal leading from the receptor pore to the inner chambers were the longest and the overlaying epidermal layers are the thickest. These results show that mormyromasts and the epidermis they are embedded in at both foveal regions differ specifically from those found on the rest of the body. The morphological specializations lead to functional specialization of the two foveae. J. Morphol., 2012. © 2012 Wiley Periodicals, Inc. 相似文献
4.
Short-timescale variability of picophytoplankton abundance and cellular parameters in surface waters of the Alboran Sea (western Mediterranean) 总被引:1,自引:0,他引:1
Jacquet Stephan; Prieur Louis; Avois-Jacquet Carol; Lennon Jean-Francois; Vaulot Daniel 《Journal of plankton research》2002,24(7):635-651
The Alboran Sea (western Mediterranean) is characterized bya well-defined hydrological structure, the Almeria (Spain)Oran(Algeria) geostrophic front. During the Almofront-2 cruise (November22, 1997 to January 18, 1998), high frequency sampling ( 相似文献
5.
Stephan J. Linke Andreas Frings Ling Ren Amadeus Gomolka Udo Schumacher Rudolph Reimer Nils-Owe Hansen Nathan Jowett Gisbert Richard R. J. Dwayne Miller 《PloS one》2015,10(3)
The impact of using a Femtosecond laser on final functional results of penetrating keratoplasty is low. The corneal incisions presented here result from laser ablations with ultrafast desorption by impulsive vibrational excitation (DIVE). The results of the current study are based on the first proof-of-principle experiments using a mobile, newly introduced picosecond infrared laser system, and indicate that wavelengths in the mid-infrared range centered at 3 μm are efficient for obtaining applanation-free deep cuts on porcine corneas. 相似文献
6.
7.
The cornea is the shield to the foreign world and thus, a primary site for peripheral infections. However, transparency and vision are incompatible with inflammation and scarring that may result from infections. Thus, the cornea is required to perform a delicate balance between fighting infections and preserving vision. To date, little is known about the specific role of antigen-presenting cells in viral keratitis. In this study, utilizing an established murine model of primary acute herpes simplex virus (HSV)-1 keratitis, we demonstrate that primary HSV keratitis results in increased conventional dendritic cells (cDCs) and macrophages within 24 hours after infection. Local depletion of cDCs in CD11c-DTR mice by subconjuntival diphtheria toxin injections, led to increased viral proliferation, and influx of inflammatory cells, resulting in increased scarring and clinical keratitis. In addition, while HSV infection resulted in significant corneal nerve destruction, local depletion of cDCs resulted in a much more severe loss of corneal nerves. Further, local cDC depletion resulted in decreased corneal nerve infection, and subsequently decreased and delayed systemic viral transmission in the trigeminal ganglion and draining lymph node, resulting in decreased mortality of mice. In contrast, sham depletion or depletion of macrophages through local injection of clodronate liposomes had neither a significant impact on the cornea, nor an effect on systemic viral transmission. In conclusion, we demonstrate that corneal cDCs may play a primary role in local corneal defense during viral keratitis and preserve vision, at the cost of inducing systemic viral dissemination, leading to increased mortality. 相似文献
8.
The population dynamics of D. galeata was studied during the period May–July of 5 successive years in Bautzen Reservoir (Germany). Sampling intervals of 3–4 days and knowledge of the egg–age distribution made it possible to calculate recruitment of the population for each sampling interval. In every year, high Daphnia densities and high Secchi depth readings (clear-water stage) were recorded in spring. In two of the 5 years, Daphnia abundance remained on a high level throughout summer, whereas in the remaining 3 years a midsummer decline of Daphnia was observed. Birth rates declined while the abundance increased in spring in every year but the timing of this decline in relation to abundance and the onset of the clear-water stage revealed no obvious pattern, distinguishing between years with or without a midsummer decline. However, cumulative recruitment did reveal a clear pattern: in years without a midsummer decline, cumulative recruitment increased slowly, but continually, starting from a low level in early May. By contrast, in years with a midsummer decline, recruitment increased strongly during one week in May, starting from a relatively high density level (>30 ind. l–1). This quick increase was followed by extended periods with low recruitment. Consequently, in these years the population was dominated by a strong peak-cohort of about the same age during the clear-water stage. If all members of this cohort, while approaching their maximum life-span, die off during a short time interval, this may have a pronounced effect on the initiation of a midsummer decline. From an extensive literature search, evidence is provided that the findings of this study represent a demographic mechanism which is of general importance for the initiation of a midsummer decline in temperate waters. 相似文献
9.
10.
K von Figura 《Current opinion in cell biology》1991,3(4):642-646
Recent studies have established that in mammalian cells insulin-like growth factor-II can couple the large mannose-6-phosphate receptor to a GTP-binding protein and that the insulin-like growth factor-II-induced activation of the GTP-binding protein is inhibited by mannose-6-phosphate and lysosomal enzymes. In mouse, the gene for the large mannose-6-phosphate receptor is maternally imprinted. 相似文献